CAUSING RECORD-BREAKING TEMPERATURES AND DANGEROUS FUEL FOR SUMMER WILDFIRES. DANA GRIFFIN, NBC NEWS. >>> NOW TO THAT CRUCIAL DEBATE BETWEEN VICE PRESIDENT HARRIS AND FORMER PRESIDENT TRUMP. THEIR FIRST AND PERHAPS ONLY SHOWDOWN. PETER ALEXANDER IS IN PHILADELPHIA WITH NEW REPORTING ON THE 11th HOUR PREPARATIONS. >> Reporter: TONIGHT VICE PRESIDENT HARRIS TOUCHING DOWN IN PHILADELPHIA. HER FACE TO FACE WITH FORMER PRESIDENT TRUMP JUST 24 HOURS AWAY. >> HOW ARE YOU FEELING? >> Reporter: CAMPAIGN SOURCES TELL NBC NEWS HARRIS AND HER TEAM ARE FOCUSING ON WAYS TO NEEDLE TRUMP, TO PROVOKE HIM, AND THAT SHE'S STUDIED PAST TRUMP DEBATE CLIPS. >> IT'S TIME TO TURN THE PAGE ON THE DIVISIVENESS. IT'S TIME TO BRING OUR COUNTRY TOGETHER. >> Reporter: BUT A KEY CHALLENGE FOR HARRIS TRYING TO PRESENT HERSELF AS THE CHANGE CANDIDATE WHEN SHE'S ALSO THE INCUMBENT VP. A NEW POLL SHOWS MORE THAN 60% OF LIKELY VOTERS WANT A MAJOR CHANGE FROM PRESIDENT BIDEN. MORE THAN HALF OF THOSE VOTERS SAY TRUMP WILL BRING THAT CHANGE. BUT ONLY 25% SAY HARRIS WILL. MEANWHILE, THE FORMER PRESIDENT AT MAR-A-LAGO DOING WHAT SOURCES DESCRIBE AS INFORMAL DEBATE PREP. AMONG THOSE ADVISING HIM FORMER DEMOCRATIC CONGRESSWOMAN TULSI GABBARD. >> WE'RE RUN BY STUPID PEOPLE. AND WE FOUND THAT OUT AT THE DEBATE WITH JOE. HOW DID THAT WORK OUT? AND WE'RE GOING TO FIND IT OUT AGAIN ON TUESDAY NIGHT. >> Reporter: A CRUCIAL CHALLENGE FOR TRUMP, WINNING BACK MORE WOMEN VOTERS. BUT THIS WARNING TODAY FROM TRUMP RIVAL TURNED SUPPORTER NIKKI HALEY. >> DONALD TRUMP AND J.D. VANCE NEED TO CHANGE THE WAY THEY SPEAK ABOUT WOMEN. YOU DON'T NEED TO GO AND TALK ABOUT INTELLIGENCE OR LOOKS OR ANYTHING ELSE. JUST FOCUS ON THE POLICIES. >> Reporter: THIS WILL BE TRUMP'S SEVENTH GENERAL ELECTION DEBATE, HARRIS'S FIRST, AND IT COULD BE THEIR ONLY SHOWDOWN. NOTABLY, THE TWO HAVE NEVER MET. TRUMP LEFT TOWN BEFORE PRESIDENT BIDEN'S INAUGURATION. LESTER? >> PETER ALEXANDER, THANK YOU. AND A TOPIC THAT COULD COME UP IN TOMORROW NIGHT'S DEBATE, THE INCREASINGLY INFLAMMATORY RHETORIC FROM FORMER PRESIDENT TRUMP ABOUT HIS PERCEIVED ENEMIES. HERE'S VAUGHN HILLYARD. >> Reporter: TONIGHT AS HE PREPARES FOR HIS CRITICAL DEBATE SHOWDOWN FORMER PRESIDENT TRUMP VOWING TO TOTALLY RESHAPE THE JUSTICE DEPARTMENT AND TARGET POLITICAL OPPONENTS. >> WE WILL COMPLETELY OVERHAUL KAMALA'S CORRUPT DEPARTMENT OF INJUSTICE. >> Reporter: HE RECENTLY REPOSTED DOCTORED IMAGES OF TOP DEMOCRATS ALONG WITH ANTHONY FAUCI AND BILL GATES IN ORANGE JUMPSUITS WITH THE CAPTION "HOW TO FEEL FIX THE SYSTEM." AND IN TRUMP'S NEW BOOK ALLEGING FACEBOOK CEO MARK ZUCKER BRERG WILL TRY TO UNLAWFULLY INFLUENCE THE 2024 ELECTION WRITING "IF HE DOES ANYTHING ILLEGAL THIS TIME HE WILL SPEND THE REST OF HIS LIFE IN PRISON." JUST THIS WEEKEND TRUMP PROMISING POSSIBLE RETRIBUTION AGAINST 2024 ELECTION ADMINISTRATORS, WRITING "LAWYERS, POLITICAL OPERATIVES, DONORS, ILLEGAL VOTERS AND CORRUPT ELECTION OFFICIALS, THOSE INVOLVED IN UNSCRUPULOUS BEHAVIOR WILL BE SOUGHT OUT, CAUGHT AND PROSECUTED AT LEVELS UNFORTUNATELY NEVER SEEN BEFORE IN OUR COUNTRY." BUT ILLEGAL VOTING IS RARE AND TONIGHT A REPUBLICAN ELECTION OFFICIAL IN ARIZONA TOLD US HE'S WORRIED. >> I'M CONCERNED WE WILL SEE POTENTIALLY PROFESSIONALS WHO ARE MORE WILLING TO BEND GENERAL RULES OF PROSECUTORIAL ETHICS OR LEGAL STANDARDS, WHO WILL OCCUPY THESE POSITIONS. >> Reporter: THIS SUMMER'S CONSEQUENTIAL SUPREME COURT RULING ALSO GAVE A PRESIDENT ABSOLUTE IMMUNITY OVER ANYTHING HE ORDERS OR SAYS TO HIS ATTORNEY GENERAL. THOUGH TRUMP'S GOP SUPPORTERS ARGUE THAT DOJ AND DEMOCRATIC PROSECUTORS ARE GOING AFTER HIM TO HURT HIS CAMPAIGN. >> MY POLL NUMBERS I BELIEVE ARE HIGHER NOW BECAUSE THE PUBLIC UNDERSTANDS IT'S A HOAX. >> Reporter: THE HARRIS CAMPAIGN RESPONDING BY SAYING THAT TRUMP WILL, QUOTE, USE HIS UNCHECKED POWERS TO PROSECUTE HIS ENEMIES. LESTER? >> ALL RIGHT. VAUGHN HILLYARD, THANK YOU. JOIN US TOMORROW NIGHT FOR COVERAGE OF THE