Seldom before has a major American politician endured greater ups and downs in his career than the former vice president from Delaware.

Elected to the U.S. Senate in 1972 at age 29, weeks before he was old enough to qualify and serve, he lost his young wife and infant daughter in a car accident. He had to be persuaded by Sen. Ted Kennedy and others to take the seat, if only as therapy after the tragedy.

He persevered for 36 years, commuting daily between Delaware and Washington, D.C., to care for his two young sons who survived the same crash.

When he became President Barack Obama’s vice president in 2009, he moved his rebuilt family including second wife, Jill, to D.C., and now is on the brink of becoming his Democratic Party’s 2020 presidential nominee.

After a dismal start to his campaign in which he fell from frontrunner to almost an also-ran in the earliest primaries, he suddenly bounced back in South Carolina, blowing away all opposition in its primary and then in subsequent state contests.

By mid-March, only Sen. Bernie Sanders of Vermont stood his way. On the verge of winning enough convention delegates to give him the nomination, it appeared only a matter of time for him to complete the task.

But then out of the blue came the great coronavirus of 2020, and its dictate of an essential nationwide shutdown of American business as usual. It has included most of the presidential election process, requiring many states to push forward their primary dates into June, only weeks before the opening of the Democratic convention in Milwaukee in md-July.

Voting by mail is being considered now to comply with social distancing, a costly and complicating process of uncertain result for the states that have not yet cast their primary ballots.

The question now is whether the delay could break the momentum the Biden campaign had built up to that time. He has resorted to seeking television time from the cable and network outlets and using a makeshift studio in his home in Wilmington to conduct what are being called virtual press conferences with called-in inquiries and no audiences.

Meanwhile, Sanders is undergoing increasing pressures from Biden and other Democratic forces to drop out of the race to assure unity against Donald Trump in the fall.

At this writing there is no sign of that happening, and in fact Sanders has been pressing the Democratic National Committee to hold another televised debate between Biden and himself.

Not surprisingly, Biden has said: “I think we’ve had enough debates. I think we should get on with this.” In his previous debate with Sanders, however, nothing appeared to have changed to alter the expected outcome.

So both men will have to wait to see what happens in the remaining primaries, in this most bizarre of recent presidential marathons.

Jules Witcover’s latest book is “The American Vice Presidency: From Irrelevance to Power.” You can respond to this column at juleswitcover@comcast.net.