Vice presidential chances: How history bodes for Biden

Joe Biden has a political imperative as he embarks on his 2020 presidential bid — to be more like Ronald Reagan circa 1980 and less like Jeb Bush in 2016.

Biden this week became the 20th major Democratic candidate to announce he's contesting the right to challenge President Trump to the White House next year, a clear favorite in early polls thanks to the national profile he's built over three decades in the Senate and eight years as President Barack Obama's No. 2.

But both former President Ronald Reagan and ex-Florida Gov. Jeb Bush were front-runners in their crowded primary fields before their races for the Republican Party's nomination ended up going in opposite directions when votes were counted. Reagan, the former California governor, beat nine Republican opponents, including then-former CIA Director George H.W. Bush and ex-Sen. Bob Dole of Kansas, a lion of the Senate. Jeb Bush, unlike his father and brother, former President George W. Bush, stumbled and became one of 16 Republican rivals vanquished by reality TV star and real estate mogul Donald Trump's bombastic campaign style.

University of Pennsylvania professor Brian Rosenwald said it was obviously ideal to be the leading candidate, but top contenders aren't immune to controversy. He cited Reagan's loss in Iowa in 1980 ahead of his win in New Hampshire as an example of how candidates sometimes "get punched in the mouth" before "they have rebounded."