WASHINGTON — In the course of four days, former Vice President Joe Biden switched the narrative of the Democratic presidential campaign from fear of a progressive (aka democratic socialist) takeover by Sen. Bernie Sanders to one of moderate liberal business as usual.

Biden’s startling South Carolina blowout over Sanders and other contenders, followed by his impressive victories in 10 of the 14 Super Tuesday primaries, at least temporarily restored the party’s normal order of things.

Sparked by Biden’s familiar optimism, geniality and unexpected public support, he capped the four-day resurrection with a grinning election-night display of self-confidence that earlier had seemed to escape him.

Tuesday night found him leading both in the national popular vote and in convention delegates won, not including California’s, where the results had not yet calculated. For the time being, it is now Sanders who is seeking to head off a possible first ballot nomination in Milwaukee in mid-July.

With Sanders as a distinct outsider in the party establishment, many regular Democrats had expressed concern that his self-description as a democratic socialist, predictably exploited by President Donald Trump in the fall, would cause his defeat and re-elect Trump.

Instead, the prospect of Biden, fired up to fulfill his promise to “beat Trump like a drum” in November, offers a more united Democratic Party in that effort.

Former New York Mayor Michael Bloomberg, who threw himself and his billions of personal wealth into the race to beat Trump, withdrew from the race Wednesday.

Biden’s comeback comes after a much-maligned campaign in which his history of personal gaffes and slips of the tongue were repeatedly raised in some news media quarters. But the sudden drama of going overnight from weak and uneven loser to energized frontrunner appears to have changed the optics of the campaign and his fortunes as well.

Always an emotional politician wearing his heart on his sleeve, Biden has often invoked his personal family narrative of peaks and valleys. The stories of his loss of his first wife and infant daughter in a car accident only days after being elected to the Senate in 1972, and the death of his elder son Beau of brain cancer in 2015, have reinforced his reputation for empathy toward others’ family losses.

In the eve of the South Carolina primary, with television cameras rolling, he told the pastor of a Charleston church whose wife was killed in a mass shooting in 2016 of his kinship with him and bereaved members of the congregation. It was a dramatic moment.

When a 2020 Democratic presidential rival, former South Bend Mayor Pete Buttigieg, subsequently bowed out and endorsed Biden, the former vice president compared him to Beau in another gesture of how his personal family history is an integral part of his political life.

Even in the recent trying episode of his son Hunter’s job on the board of a Ukrainian energy firm, used by Trump to damage the father in the 2020 election, Joe Biden declined to criticize his other son, regardless of any political fallout to himself.

His deep and open allegiance to his family, spoken or otherwise, is a reality that has been heart of his public life over his years of service in the Senate, as vice president and now as presidential candidate. It is, to many in his home state of Delaware, a measure of his commitment. There, he often gives “my word as a Biden” as personal commitment to what he promises.

He obviously hopes now it will help deliver him the presidency, against an incumbent who daily demonstrates that his own word is worthless. Whether that difference will matter, though, is uncertain.

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