PHILADELPHIA (AP) — Vice President Kamala Harris introduced Minnesota Gov. Tim Walz as her running mate Tuesday at a raucous rally in Philadelphia, turning to an affable longtime politician who Democrats hope can keep newfound party unity alive in a presidential campaign barreling toward Election Day. The two made their first public appearance just hours after Harris announced Walz as her vice presidential pick to take on the Republican ticket of former President Donald Trump and Ohio Sen. JD Vance. “Since the day that I announced my candidacy, I set out to find a partner who can help build th…