>>> TONIGHT, THE FULL JURY SELECTED IN DONALD TRUMP'S TRIAL. THEY SAID WE HAVE OUR JURY AFTER SEATING THE 12 PEOPLE THAT WILL DECIDE THE FORMER PRESIDENT'S FATE, INCLUDING AN INVESTMENT BANKER, A RETIRED PRIVATE WEALTH MANAGER AND SPEECH THERAPIST AND THE TWO JURORS THAT WERE DISMISSED, A NURSE AND I.T. WORKER. WHY THEY WERE EXCUSED. OUR TEAM AT THE COURTHOUSE. >>> ALSO TONIGHT, COLUMBIA UNIVERSITY'S PRESIDENT CALLING IN THE NYPD TO ARREST MORE THAN 100 PRO-PALESTINIAN PROTESTERS A DAY AFTER SHE TESTIFIED BEFORE CONGRESS ABOUT ANTI-SEMITISM ON CAMPUS. >>> THE WIDESPREAD 911 OUT AGE IN FOUR STATES. PEOPLE UNABLE TO CALL FOR HELP. IT WAS TRACED TO A SINGLE LIGHT POLE. >>> THE 18-YEAR-OLD ARRESTED IN MARYLAND THREATENING TO SHOOT UP SCHOOLS. THE 129-PAGE DOCUMENT AND MORE THAT LED A FRIEND TO CALL POLICE. >>> THE CLOSE CALL AT REAGAN NATIONAL AIRPORT. TWO PLANES NEARLY COLLIDING ON THE RUNWAY. YOU'LL HEAR THE FRANTIC CALL FROM THE TOWER. >>> 15 MEMBERSER OF THE ALLMAN BROTHERS BAND, REMEMBERING THE ICONIC DICKEY BETTS. >> ANNOUNCER: THIS IS NBC "NIGHTLY NEWS" WITH LESTER HOLT. >>> GOOD EVENING AND WELCOME. THE TRUMP HUSH MONEY TRIAL IS SPEEDING TOWARDS OPENING STATEMENTS TO NIGHT MORE QUICKLY THAN MANY IMAGINED WITH 12 JURORS NOW SELECTED TO HEAR THE CASE. AND ONE OF SIX ALTERNATE JURORS ALSO CHOSEN LATE TODAY. THE RAPID ASSEMBLY OF A JURY PANEL CAME AFTER THE PROCESS APPEARED TO SUFFER A SERIOUS SETBACK EARLIER WHEN TWO PREVIOUSLY SELECTED JURORS WERE DISMISSED FROM THE CASE. ONE WHO HAD SECOND THOUGHTS ABOUT HER ABILITY TO BE IMPARTIAL, THE OTHER OVER AN APPARENT FAILURE TO DISCLOSE INTERACTIONS WITH LAW ENFORCEMENT. THE MANHATTAN JURY WILL SIT IN JUDGEMENT OF WHETHER MR. TRUMP ILLEGALLY FALSIFIED BUSINESS RECORDS AS PART OF A SCHEME TO CONCEAL HUSH MONEY PAYMENTS TO A PORN STAR WITH WHOM HE'S ALLEGED TO HAVE HAD AN AFFAIR. ALLEGATIONS HE DENIES. LAURA JARROD HAS LATE DEVELOPMENTS. >> Reporter: TONIGHT, A FULL JURY OF 12 NOW SWORN IN IN FORMER TRUMP'S HUSH MONEY CRIMINAL TRIAL. AFTER THE DAY BEGAN WITH DRAMA SURROUNDING TWO JURORS DISMISSED. THE FULL JURY NOW INCLUDING AN INVESTMENT BANKER, SECURITY ENGINEER, RETIRED PRIVATE WEALTH MANAGER, SPEECH THERAPIST, PHYSICAL THERAPIST, SOMEONE IN E-COMMERCE AND PRODUCT DEVELOPMENT MANAGER. >> I'VE BEEN HERE ALL DAY ON A TRIAL THAT REALLY IS A VERY UNFAIR TRIAL. EVERYONE IS WATCHING THIS NEW YORK SCAM. >> Reporter: MR. TRUMP ARRIVING WITH SEVEN JURORS SWORN IN ONLY TO SEE THAT NUMBER QUICKLY GO DOWN TO FIVE AFTER AN ONCOLOGY NURSE WHO SAID DURING QUESTIONING THAT NO ONE WAS ABOVE THE LAW. I'M HERE TO JUST HEAR THE FACTS, TELL THE JUDGE TODAY, SHE HAD CONCERNS SHE COULD NOT BE IMPARTIAL ABOUT MR. TRUMP. AND WORRIED ABOUT HER IDENTITY BECOMING PUBLIC AFTER LOVED ONES FIGURED OUT SHE HAD BEEN IMPANELLED. THE OTHER JUROR, AN OLDER I.T. CONSULTANT WHO CALLED THE NOMINEE FASCINATING IN COURT US IS EXCUSED TO DAY AFTER PROSECUTORS SAID HE WAS ARRESTED FOR TEARING DOWN CONSERVATIVE POLITICAL ADS DECADES AGO. AND DID NOT REVEAL IT ON HIS JUROR QUESTIONNAIRE. LATE TODAY, THOSE ADDITIONAL JURORS SELECTED TO SERVE. AMONG THEM, AN INVESTMENT BANKER WHO SAID HE FOLLOWED MR. TRUMP'S TRUTH SOCIAL POST AND HAS SEEN QUOTES FROM "THE ART OF THE DEAL" BUT HAD NOT READ IT. THE RETIRED PRIVATE WEALTH MANAGER WHO SAYS DOES HE YOGA EVERY MORNING AND THAT SPEECH THERAPIST SAYING OF MR. TRUMP, I TEND NOT TO AGREE WITH A LOT OF HIS POLITICS AND HIS DECISIONS AS A PRESIDENT. BUT SAID SHE CAN BE IMPARTIAL. AT ONE POINT, A JUROR EVEN APOLOGIZING TO THE FORMER PRESIDENT FOR HER PAST CRITICISMS OF HIM ON SOCIAL MEDIA. SHE WAS DISMISSED. TODAY'S EVENTS UNDERSCORING THE CHALLENGES OF SEATING A JURY IN DEEP BLUE MANHATTAN WHERE 85% OF PEOPLE VOTED FOR PRESIDENT BIDEN. WHEN THE POOL OF 96 JURORS WAS ASKED THIS MORNING IF THEY COULD BE IMPARTIAL IN JUDGING THE LIKELY REPUBLICAN NOMINEE, NEARLY 50 HANDS WENT UP SAYING THEY COULD NOT. AND THEY WERE DISMISSED. THIS WOMAN WAS AMONG THEM. >> I COULDN'T BE IMPARTIAL. HAS A HISTORICAL CASE. THIS IS GOING TO DEFINE SO MANY THINGS. BUT AT THE SAME TIME, OUR JOB AS A JUROR IS TO BE IMPARTIAL. >> Reporter: MR. TRUMP SOUNDING OFF ABOUT THE JURY SELECTION PROCESS WRITING, "HE WAS GIVEN THE SECOND WORST VENUE IN THE COUNTRY." HE'S ACCUSED OF DOCTORING INTERNAL BUSINESS RECORDS TO HIDE A REIMBURSE PAYMENT FROM MICHAEL COHEN WHO PAID OFF STORMY DANIELS AHEAD OF THE 2016 ELECTION SO SHE COULDN'T GO PUBLIC ABOUT AN AFFAIR. MR. TRUMP DENIES ANY SEXUAL RELATIONSHIP WITH DANIELS AND PLEAD NOT GUILTY. >> AND THE JURY IS SEVEN SEVEN MEN AND FIVE WOMEN. THERE WAS ONE ALTERNATE SELECTED? >> Reporter: THAT'S RIGHT. FIVE MORE TO GO. THE MOST REMARKABLE MOMENTS HAPPENING AT THE VERY END OF THE DAY. THE PROSECUTION SAID THEY WOULD NOT TURN OVER THE NAMES OF THE FIRST THREE WITNESSES THAT IT PLANS TO CALL AT THIS TRIAL. THAT IS SOMETHING THAT IS ROUTINELY DONE SO THE DEFENSE CAN PREPARE. THE PROSECUTION SAYING THEY'RE SO WORRIED THAT MR. TRUMP WILL SAY SOMETHING ABOUT THEM ON SOCIAL MEDIA AND THE JUDGE IN THIS CASE AGREES, LESTER. >> ALL RIGHT. LAURA, THANK YOU. >>> WE TURN NOW TO A STUNNING SCENE IN COLUMBIA UNIVERSITY IN NEW YORK TODAY. POLICE IN RIOT GEAR MOVING IN TO CLEAR AN ENCAMPMENT OF STUDENTS PROTESTING THE WAR IN GAZA. DOZENS ARRESTED. ANTONIA HILTON IS THERE. DESCRIBE THE SEEN FOR US. >> Reporter: LESTER, PRESS IS NOT BEING ALLOWED ON CAMPUS. WHAT YOU'RE SEEING HERE ARE PROTESTS THAT SPILLED OVER TO THE PUBLIC STREETS. PROTESTS THAT, AS YOU CAN SEE, APPEAR TO BE FAR FROM OVER. CONFRONTATION AT COLUMBIA TODAY. POLICE REMOVING PROTESTERS FROM CAMPUS, CITING EXTRAORDINARY CIRCUMSTANCES. COLUMBIA UNIVERSITY PRESIDENT CALLED IN THE NYPD TO CLEAR AN ENCAMPMENT, A PRO-PALESTINIAN DEMONSTRATORS. IT SET UP WEDNESDAY MORNING, THE SAME DAY SHE TESTIFIED ON CAPITOL HILL ABOUT ANTI-SEMITISM ON CAMPUS. >> WE MUST UPHOLD FREEDOM OF SPEECH. IT IS ESSENTIAL TO OUR ACADEMIC MISSION. WE CANNOT AND SHOULD NOT TOLERATE ABUSE OF THE PRIVILEGE TO HARASS AND DISCRIMINATE. >> Reporter: IN THE LETTER TO THE UNIVERSITY, SHE NOTED, PROTESTS HAVE A STORIED HISTORY AT COLUMBIA. ANTI-VIETNAM DEMONSTRATORS TOOK OVER BUILDING ON CAMPUS IN 1968. BUT IN ASKING FOR HELP FROM THE POLICE, SHE SAID, THE ENCAMPMENT AND RELATED DISRUPTIONS HAD A CLEAR AND SUBSTANTIAL DANGER TO THE FUNCTIONING OF THE UNIVERSITY. >> WE'RE RISKING OUR ACADEMIC STANDING JUST TO, LIKE, SHOW THE ADMINISTRATORS THAT WE ARE NOT OKAY WITH THEIR DECISION. >> Reporter: SEVERAL DEMONSTRATOR STOMPING ON AN ISRAELI FLAG. SOME STUDENTS SAYING THEY FEEL UNSAFE ON CAMPUS. >> I FEEL AS THOUGH PEOPLE ARE KIND OF WEAPONIZING ANTI-SEMITISM. >> Reporter: DEMONSTRATORS TELLING US THEY PLAN TO KEEP THEIR PROTESTS GOING DESPITE THE POLICE PRESENCE. DO YOU FEEL THIS ADMINISTRATION HAS CLAMPED DOWN ON STUDENTS AND FACULTY MEMBERS? >> 100%, YES. I BELIEVE THAT. >> Reporter: NEW YORK CITY'S MAYOR TONIGHT SAYING POLICE MADE MORE THAN 100 ARRESTS ON A CAMPUS SEVERELY DIVIDED. ANTONIA HILTON, NBC NEWS, NEW YORK. YORK. >>> THE GOVERNMENT IS INVESTIGATING WHY CRITICAL 911 CENTERS IN MULTIPLE STATES WERE KNOCKED OFFLINE. EXPERTS SAY IT EXPOSES A NATIONAL SECURITY VULNERABILITY. HERE IS TOM COSTELLO. >> Reporter: BREAKING THIS AFTERNOON, HONOLULU POLICE REPORTING A BRIEF 911 OUTAGE IN THE CITY COMING AFTER MORE OUTAGES WEDNESDAY NIGHT ON THE MAINLAND. >> YOU MAY HAVE DIFFICULTY REACHING US INTERNALLY. WE'RE HAVING DIFFICULTY RECEIVING 911 CALLS. >> Reporter: 6:00 P.M. CENTRAL TIME, MULTIPLE 911 CENTERS CUT OFF, IN PARTS OF FOUR STATES. SOUTH DAKOTA, NEBRASKA, NEVADA, AND TEXAS. SEVERAL CALL CENTERS PUSHED OUT EMERGENCY ALERTS TELLING LOCALS TO USE THEIR CELL PHONES OR TEXT FOR HELP. >> TO OUR KNOWLEDGE, WE HAVE NEVER EXPERIENCED AN OUTAGE OF THIS MAGNITUDE. >> Reporter: SERVICE PROVIDER LOOMA TECHNOLOGIES BLAME THREE OUTAGES ON A CUT FIRE LINE DUE TO A THIRD-PARTY COMPANY INSTALLING A LIGHT POLE WRITING, WE RESTORED ALL SERVICES IN APPROXIMATELY 2 1/2 HOURS. >> WE'RE DEALING WITH 911 AND LAST-CENTURY TECHNOLOGY. WE'RE IN THE 21st CENTURY. WE NEED TO ENSURE THAT OUR 911 SYSTEMS ARE CURRENT TECHNOLOGY. >> Reporter: WHILE AN ISOLATED VENT, THE OUTAGE UNDERSCORES AN URGENT CONCERN. >> 911, WHAT IS THE EMERGENCY? >> Reporter: U.S. CYBERSECURITY WARNED THAT HACKERS WANT TO EXPLOIT VULNERABILITIES TO DEGRADE 911 SERVICE. AT RISK, SENSITIVE DATA THAT COULD AFFECT EMERGENCY RESPONSIBILITIES. >> WAS ANYBODY INJURED? >> Reporter: RANSOMWARE ATTACKS ON BUCKS COUNTY, PENNSYLVANIA, FORCED DISPATCHERS TO REVERT TO MANUAL SYSTEMS. IN 2019, 911 CENTERS IN A DOZEN STATES WERE PARALYZED. NOW AMID HEIGHTENED GLOBAL TENSIONS AND DIVISIVE ELECTION LOOMING AT HOME, CONCERN THAT CRITICAL EMERGENCY COMMUNICATIONS CAN EASILY BE UNDERMINED. CHRIS KREBS IS THE FORMER GOVERNMENT'S FORMER CYBERSECURITY CHIEF. >> THE HOMELAND, AS WE SAY, IS NO LONGER A SANK WARY. WE REALLY HAVE TO BAKE IN CYBERSECURITY RESILIENCE MEASURES INTO EVERY BUSINESS PLAN, EVERY OPERATIONAL PLAN. >> Reporter: TOM COSTELLO, NBC NEWS, WASHINGTON. >>> A MARYLAND TEENAGER IS UNDER ARREST CHARGED WITH THREATENING MASS VIOLENCE. WE REPORT ON HOW A FRIEND RAISED RED FLAGS. >> Reporter: TONIGHT, 18-YEAR-OLD ALEX YI IS IN CUSTODY AFTER MARYLAND POLICE SAY HE THREATENED TO SHOOT UP HIS HIGH SCHOOL. ALL DETAILED IN A 129-PAGE MEMOIR THAT DISCUSSED KILL STUDENTS. HE SHARED THE DOCUMENT WITH A FRIEND. HE SAID IT WAS A WORK OF FICTION. ACCORDING TO CHARGING DOCUMENTS THAT, FRIEND CALLED THE BALTIMORE COUNTY POLICE BECAUSE THEY BELIEVED A SCHOOL SHOOTING WAS IMMINENT. >> I'M WORRIED. I DON'T KNOW WHAT TO THINK. I DON'T KNOW WHO IN THIS SCHOOL IS GOING THROUGH SOMETHING THAT I MAY NOT SEE. >> Reporter: YI HAD BEEN ATTENDING THE SCHOOL VIRTUALLY SINCE 2022 AND SPENT TIME IN A PSYCHIATRIC FACILITY DUE TO SUICIDAL AND HOMICIDAL THOUGHTS ACCORDING TO POLICE. IN THE MEMOIR, HE DETAILED HOW HE WOULD DO IT. AND WHO HIS IDEAL VICTIMS WOULD BE. THE DOCUMENT P OZ BY SAYING IT IS A WORK OF FICTION BUT YI'S FRIEND TOLD POLICE THE BOOK MAIN CHARACTER MIRRORED HIM IN MANY WAYS. THEY WERE BOTH ASIAN AND FELT BULLIED BY OTHER STUDENTS. AUTHORITIES DETAILED OTHER RED FLAGS THAT LED TO THE MISDEMEANOR CHARGE INCLUDING MEDICAL OFFICIALS PREVIOUSLY REPORTING THAT YI WAS PREOCCUPIED WITH SELF-HARMING, SCHOOL SHOOTINGS AND EXPLOSIVES. HIS INSTAGRAM CHAT LOG HAD A REFERENCE OF WANTING TO BE A FAMOUS SERIAL KILLER. HIS ONLY FIRE ARM WAS A BB GUN, THE INTERNET SEARCHES INCLUDED GUN RANGED NEAR ME AND SEARCHES ABOUT OTHER SCHOOL SHOOTINGS. YI'S FATHER SAID HE WAS NOT CONCERNED ABOUT HIS SON'S MENTAL HEALTH STATUS AND AWARE WHAT HE WAS WRITING A NOVEL. HE IS CURRENTLY BEING HELD IN CUSTODY WHERE HE AWAITS A BOND HEARING. LESTER? >> THANK YOU. >>> LET'S TURN TO THE 2024 PRESIDENTIAL CAMPAIGN. TODAY PROMINENT MEMBERS OF THE KENNEDY FAMILY ENDORSED PRESIDENT BIDEN EVEN THOUGH ROBERT KENNEDY JR. IS RUNNING AGAINST HIM. WE HAVE THIS REPORT. >> Reporter: TODAY WITH HIS OPPONENT STUCK IN COURT, PRESIDENT BIDEN ON THE ATTACK IN BATTLEGROUND PENNSYLVANIA. >> THE 2024 ELECTION IS ABOUT TWO FUNDAMENTALLY DIFFERENT VISIONS FOR AMERICA. TRUMP'S VISION IS ABOUT ANGER HATE AND RETRIBUTION. >> Reporter: THE CAMPAIGN TOUTING THE ENDORSEMENT OF 15 KENNEDY FAMILY MEMBERS, EVEN ONE OF THEIR OWN, ROBERT F. KENNEDY JR. IS RUNNING AGAINST HIM. AS AN INDEPENDENT. >> THE BEST WAY FORWARD FOR AMERICA IS TO RE-ELECT PRESIDENT BIDEN AND KAMALA HARRIS TO FOUR MORE YEARS. >> Reporter: RESPONDING TO HIS FAMILY'S ENDORSEMENT OF HIS OPPONENT, RFK JR. POSTED ON SOCIAL MEDIA, WE'RE DIVIDED IN OUR OPINION BUT UNITED IN OUR LOVE FOR ONE ANOTHER. THE ENVIRONMENTAL LAWYER AND ANTI-VACCINE ACTIVIST FIRST RAN AS A DEMOCRAT, NOW KENNEDY'S INDEPENDENT CAMPAIGN IS POLLING ABOVE 10% IN A FEW KEY SWING STATES WHERE BIDEN IS TRAIL TRUMP. DEMOCRATS ARE AGGRESSIVELY ATTACKING THIRD-PARTY CANDIDATES LIKE KENNEDY WHOM THEY VIEW AS A THREAT TO PRESIDENT BIDEN'S RE-ELECTION IT'S NOT CLEAR WHICH CANDIDATE PRESIDENT BIDEN OR FORMER PRESIDENT TRUMP WOULD LOSE MORE VOTES TO RFK JR. KENNEDY SAID THIS IN FEBRUARY. >> I HOPE TO DRIVE EQUAL NUMBERS FOR BOTH OF THEM. I THINK AT THIS POINT I'M DRAWING MORE FROM PRESIDENT TRUMP. >> Reporter: A SOURCE FAMILIAR WITH THE BIDEN CAMPAIGN PLANNING SAID THE RUNNING OUT FY END SPEAKER JOHNSON SAYS THAT HE SUPPORTS FUNDING FOR UKRAINE EVEN IF IF IT COSTS HIM HIS JOB. LESTER? >> RYAN NOBLES, THANK YOU. >>> IN 60 SECONDS, URGENT CALLS FROM THE CONTROL TOWER. >> STOP! >> AS TWO PLANES ON A COLLISION COURSE AVOID HITTING EACH OTHER WITH LITTLE TIME TO SPARE. I. >>> BACK NOW WITH THE SCARY CLOSE CALL AT REAGA >>> BACK NOW WITH THE SCARY CLOSE CALL AT REAGAN NATIONAL AIRPORT NEAR WASHINGTON, D.C. TWO PLANES NEARLY COLLIDING ON THE RUNWAY. EMILY WITH WHAT WENT WRONG. >> Reporter: A HAIR RAISING MOMENT TODAY ON ONE OF AMERICA'S BUSIEST RUNWAYS. >> STOP. STOP! >> Reporter: AN AIR TRAFFIC CONTROLLER FRANTICALLY TELLING A SOUTHWEST PLANE TO STOP. >> WE STOPPED. WE WERE CLEARED TO CROSS RUNWAY 4. >> Reporter: AFTER IT WAS CLEARED TO TAXI ACROSS THE RUNWAY. >> CLEAR AT FOUR. TAKEOFF. >> Reporter: A JETBLUE PLANE WAS ABOUT TO TAKE OFF ACCORDING TO THE FAA. BUT THEN ALSO SUDDENLY TOLD TO ABORT. >> STOP. >> STOP! >> Reporter: A SOURCE SAYS THE PLANES CAME LESS THAN 1,000 FEET OF EACH OTHER. >> SOMETHING WENT AMISS CAUSING ONE CONTROLLER TO CLEAR THE AIRPLANE TO TAKE OFF AND ANOTHER GROUND CONTROLLER CLEARING THE SOUTHWEST AIRLINES TO CROSS THAT SAME ACTIVE RUNWAY. SO, TO ME, IT LOOKS LIKE IT'S WHAT THE FAA CALLS AN OPERATIONAL AIR INVOLVING A AIR OPERATIONAL ERROR INVOLVING AN AIR TRA AIR TRAFFIC CONTROL ISSUE. >> Reporter: AFTER A STRING OF NEAR MISSES, A SAFETY REVIEW FOUND OVERTIME IS AT A HISTORICALLY HIGH LEVEL FOR AIR TRAFFIC CONTROLLERS. AND CHALLENGES INCLUDING STAFFING SHORTAGES HAVE CAUSED AN EROSION OF SAFETY MARGIN THAT'S MUST BE URGENTLY ADDRESSED. TONIGHT, THE FAA REPORTS SERIOUS RUNWAY INCURSIONS ARE TRENDING DOWN. >> STOP! STOP! >> Reporter: REGARDING THE LATEST SCARE, BOTH AIRLINES SAY THEY'RE WORKING CLOSELY WITH FEDERAL INVESTIGATORS TO DETERMINE WHAT WENT WRONG. >>> AND NEXT, POLLEN SEASON, WHAT IS CAUSING SUCH AN EYE-WATERING SPRING FOR SO MANY? >>> ALLERGY SUFFERERS, IT IS NOT YOUR IMAGINATION. FOR MANY, ALLERGY SEASON IS GETTING WORSE. ANNE THOMPSON EXPLAINS WHY AND WHAT YOU CAN DO ABOUT IT. >> Reporter: THIS IS WHERE DAVID LOVES TO BE, OUTDOORS PLAYING SPORTS. BUT HIS WORSENING ALLERGIES MAKE FUN, EVEN SCHOOL DIFFICULT FOR THE 8-YEAR-OLD. >> HIS EYES ARE REALLY BLOODSHOT. HE IS SO UNCOMFORTABLE. WE KEPT HIM HOME. HI, DAVID. >> Reporter: A TRAINED ALLERGIST SEES HIM IN HER CLINIC. >> YOUR EYES ARE ITCHY AND WATERY? WE HAVE MORE PATIENTS COMING IN. >> Reporter: AT UNIVERSITY OF MICHIGAN, ALEX IS PUTTING UP A POLLEN COUNTER TO TRACK THE TREND DRIVEN BY CLIMATE CHANGE. >> CLIMATE CHANGE IS MAKING POLLEN INCREASE. IT IS INCREASING IN MAGNITUDE OF POLLEN AND THE LENGTH AND DURATION OF THE POLLEN. THERE IS AN EXAMPLE OF A NORMAL POLLEN GRAIN. >> Reporter: THE POLLEN SEASON IS ALREADY 20 DAYS LONGER AND CONCENTRATIONS UP 21% AND THE SEVERE THUNDERSTORMS AND CHANGING CLIMATE BREAK UP THE POLLEN INTO SMALLER PIECES THAT GO DEEP INTO THE BODY. >> WHILE THE LARGE POLLEN GRAINS ARE STOPPED BY THE UPPER RESPIRATORY SYSTEM, THE TINIER ONES CAN GET INTO YOUR LUNGS. THEY CAN TRIGGER MORE RESPIRATORY DISTRESS. >> THIS IS COMMON RAGWEED. >> Reporter: ON THE POLLEN GRAINS, COLUMBIA'S PROFESSOR SEES MORE PROTEINS, A TROUBLED SIGN FOR ALLERGY SUFFERERS. >> IF THERE IS MORE OF THAT FOREIGN SUBSTANCE, YOU'LL FEEL A STRONGER RESPONSE. >> Reporter: PROTEINS MAKING THE POLLEN MORE POTENT, MULTIPLIED BY THE CARBON DIOXIDE FUELING CLIMATE CHANGE. THE CARBON DIOXIDE IS CHANGING THE CHEMISTRY OF THE POLLEN? >> YES. EXACTLY. >> Reporter: TO KEEP THE POLLEN OUTSIDE, TAKE OFF YOUR SHOES BEFORE GOING IN. WASHING YOUR HANDS AND FACE AND WIPING DOWN YOUR PHONE, GLASSES AND SUNGLASSES. DAVID USES A TRAY OF MEDICINES TO COPE AS HIS MOM WORRIES HIS ALLERGIES WILL GET WORSE. >> SCARES ME BECAUSE I SEE HOW MUCH HE SUFFERS FROM IT EVERY YEAR. >> Reporter: WITH NO RELIEF IN SIGHT. NBC NEWS. >>> AND THAT IS "NIGHTLY NEWS." JOIN US TOMORROW FOR OUR INTERVIEW OF IRAN'S FOREIGN MINISTER. THANK YOU FOR WATCHING, EVERYONE. I'M LESTER HOLT.