Sooner or later, it was bound to happen. The Democratic contest for the party’s 2020 presidential nomination has begun to pivot from the competition among self-identified progressive candidates to cutting Joe Biden’s wide early lead in the polls among the 23-candidate pack.

It comes after weeks or months of aiming to diminish the grip of Vermont Sen. Bernie Sanders on the left side of the party, solidified in his strong 2016 candidacy as a professed democratic socialist outsider.

The weapon of choice is a carryover from Biden’s failed 1988 presidential bid, in which he was an early casualty amid allegations of plagiarism. He borrowed without attribution the words of British politician Neil Kinnock to color a description of his own humble beginnings in Scranton, Pa.

In the Iowa caucus contest that year, Biden, who had previously, often and correctly attributed the borrowing to Kinnock, used it this time without the specific attribution and paid dearly for it.

The campaign manager of a rival Democratic candidate, Massachusetts Gov. Michael Dukakis, leaked a video of the instance to the press. It triggered an unraveling of the Biden campaign while he also was chairing a critical Supreme Court hearing on the nomination of Judge Robert Bork.

Bork was regarded then among many Democrats as rigidly right-wing and a threat to the Roe v. Wade ruling upholding women’s right to abortion.

Biden didn’t favor Bork’s nomination, but as chairman of the Senate Judiciary Committee he vowed to give him a fair hearing. His decision to abandon his presidential bid came critically in that context. He returned to Washington and continued Bork’s confirmation hearings.

In late October 1988, Bork was rejected by a vote of 58-42, the widest margin ever suffered a Supreme Court nominee. Biden said later that he had had to make a choice “between my campaign and Bork. … I didn’t want to be a little asterisk in history that I set out to save my rear end and Bork got on the Court.”

Biden’s wife, Jill, later observed that also at stake was her husband’s reputation for integrity, which he referenced in his oft-used phrase, “my word as a Biden.” She said: “He needed to be vindicated. It was about Bork, it was about Bork’s politics, but it also was about Joe.” She added: “Of all things for him to get out of the race for, it was to be attacked for his character.”

Biden returned to the Senate as a legislative workhorse and bided his time — until now, when he finds himself the Democratic frontrunner in the polls for 2020.

Yet with reports of staff aides appropriating others’ words to explain his policy positions, his rivals for the party nomination are back on the trail to discredit his “word as a Biden.” And, once again, he must defend himself against yet another assault on his integrity.

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Jules Witcover is a nationally syndicated columnist.