She's already broken barriers, and now Kamala Harris could shatter several more after President Joe Biden abruptly ended his reelection bid and endorsed her. Biden announced Sunday that he was stepping aside after a disastrous debate performance catalyzed fears that the 81-year-old was too frail for a second term. If Harris becomes the Democratic nominee and defeats Republican candidate Donald Trump in November, she would be the first woman to serve as president. Professor Barbara Perry, with the University of Virginia's Miller Center for Presidential Studies, told the Associated Press that the barriers Harris broke once being selected as Biden's running mate, could continue to fall. "Just as she broke barriers to become the first woman of color to serve as vice president," Perry said, "she would bring those characteristics to the top of the ticket of a major party, one of the two major parties." Vice presidents are always in line to step into the top job if the president dies or is incapacitated. However, Harris has faced an unusual level of scrutiny because of Biden’s age. He was the oldest president in history, taking office at 78 and announcing his reelection bid at 80. Harris is 59. "In presidential years, she's very youthful, and she certainly looks youthful and has a youthful energy and sparkle about her," Perry said. Harris' nomination as the Democratic candidate is not a foregone conclusion, and there have been suggestions that the party should hold a lightning-fast “mini primary” to consider other candidates before its convention in Chicago next month. Even before Biden's endorsement, Harris was widely viewed as the favorite to replace him on the ticket. Perry believes gender, rather than race, may prove a bigger challenge for Harris. From time of George Washington, Perry said, there is a paternal model of presidents. "It's too important an office to exclude half of the American population," Perry believes. Perry said Republicans are likely to reprise personal attacks against Harris that they used during the 2020 campaign.