US President Joe Biden announced on Sunday that he is withdrawing from the race to be president for a second term, a historic decision that throws the Democratic Party into upheaval as Republican rival Donald Trump’s campaign gains steam. Biden said that Vice President Kamala Harris had his “full support” to replace him on the ballot in November’s election. He also said that he will finish out the remainder of his term, which ends in January. But with the party’s presumptive nominee now gone and just over 100 days to go, the clock is ticking for Democrats to begin the fraught process of replac…