Former Vice President Joseph R. Biden Jr. announced Thursday that he would seek the Democratic nomination to challenge President Trump in 2020, casting the election as a national emergency and asking Democrats to put the task of defeating Mr. Trump above all their other ambitions.
In a three-and-a-half minute video that focused on excoriating Mr. Trump, Mr. Biden presented himself as a steely leader for a country wracked by political conflict. Unlike the wide field of Democrats competing for the affections of the left, Mr. Biden avoided almost any talk of policy or ideology, signaling that he believes voters will embrace him as a figure of stability and maturity even in a partisan primary election.
In doing so, Mr. Biden, 76, is making a bet of sorts that the Democratic Party’s leftward shift in recent years has been greatly overstated, and that the moral clarity of his rhetoric and his seeming strength as a general election candidate will overpower other considerations for Democratic voters who tend to prize youth, diversity and unapologetic liberalism.
Laying out for the first time why he wanted to run for president, Mr. Biden invoked the white supremacist march through Charlottesville, Va., that ended in bloodshed in 2017, and Mr. Trump’s comment that there were “very fine people on both sides.” In that moment, Mr. Biden said in the video, “I knew the threat to our nation was unlike any I’d ever seen in my lifetime.”