Let me be perfectly clear: Sen. Bernie Sanders has lost the Democratic presidential nomination.

Barring Joe Biden forgetting his own name or being made into a hamburger by anti-dairy activists, Sanders has no credible chance after another primary-night trouncing on Tuesday. What Sanders did in Burlington, Vt., on Wednesday, therefore, was not a continuation of his presidential campaign but the beginning of a new campaign: that of spoiler.

And so today, I begin a new feature: the Spoiler Watch. It will track the campaign of vanity and self-aggrandizement the once-idealistic Sanders candidacy has now become. Everything Sanders does from this point on — until he eventually (hopefully) throws his support to Biden — will be to the benefit of a grateful President Trump.

Trump won the presidency, in part, because disaffected Sanders voters never embraced Hillary Clinton after the Vermont independent’s scorched-earth campaign in the 2016 primary. Now, he’s poised to do it again. He must not be allowed to succeed.

Sanders, in his speech on Wednesday, began with the right tone: “Donald Trump is the most dangerous president in the modern history of our country and he must be defeated.”

Sanders then went on to focus on Biden, naming the Democrat 13 times (compared to four mentions of Trump).

“Joe, what are you going to do?” Sanders asked, over and over, announcing his intention to re-litigate in Sunday’s debate the same issues — health care, income inequality, climate change — that have been debated thoughtfully and thoroughly to date.

Sanders admitted that Tuesday “was obviously not a good night” and that “we are currently losing the delegate count” and the “electability” argument. But, as in 2016, he said people should focus on things other than delegates.

Republican Tommy Blackwood of North Charleston, S.C. wants President Trump to stay in office, so he's trying to disrupt the Democratic primary race. (The Washington Post)

“Poll after poll, including exit polls, show that a strong majority of the American people support our progressive agenda,” he declared, and “we are winning the generational debate.”

Sanders returned to his old chestnut about a phantom Democratic “establishment” conspiring to deprive him of what is rightly his. “Today, I say to the Democratic establishment: In order to win in the future, you need to win the voters who represent the future” and not “simply be satisfied by winning the votes of people who are older.”

Thankfully, Sanders’s tone was not as caustic as it has been. But it takes a certain amount of chutzpah for a guy to cite polls when the polls that actually matter — primaries — have gone emphatically against him. It takes even more chutzpah for a guy who has held office for 40 years (30 in Congress) to pretend he’s not part of the political firmament. And it’s the pinnacle of chutzpah to suggest that he alone speaks for young people when there’s little evidence of the youth revolution he advertised.

To the extent turnout is up in the 2020 primaries over 2016, it seems to be to the advantage of Biden. While Sanders had momentum against Clinton in 2016, the momentum now belongs to the former vice president. Yes, Sanders has done better among young voters, but when you put the whole Democratic electorate together — young, old, black, white, brown, liberal, moderate, urban, suburban — Biden has come out the clear winner.

To overcome Biden’s delegate lead, The Post’s Philip Bump calculates, Sanders would need to beat Biden by an average of 12 percentage points in remaining contests. But Sanders trails Biden nationally by nearly 20 percentage points and by 40 points in Florida, which votes next week.

Sanders could have declared victory Wednesday and dropped out of the race. He has succeeded in pushing the Democratic Party to the left, and his differences with Biden are less about ends than means. As Rep. Ro Khanna (D-Calif.), a Sanders supporter, said this week: “Bernie Sanders won the idea primary.”

Yet Sanders, instead, extends the fight. Only ugliness this way lies.

There will be more of the suggestions from Sanders’s supporters that the gaffe-prone Biden is senile. There will be more conspiracy theories about the hidden hand of the establishment — not actual voters — powering Biden’s victory. And there will be more of what Elizabeth Warren called the “organized nastiness” from Sanders’s supporters.

In exit polls on Tuesday in Michigan, Missouri and Washington, 8 in 10 Sanders supporters said they would support the eventual nominee. If the goal is to beat Trump, Sanders should be persuading the two holdouts to support Biden, not encouraging bitterness among the eight.

Khanna and others who endorsed Sanders now risk being enablers of his spoiler campaign. They ought to remind him of the promise he made just last month: “If I, or anybody else, goes into the Democratic convention with a substantial plurality, I believe that individual, me or anybody else, should be the candidate of the Democratic Party.”

Excluding the unimaginable, Biden will be that candidate. Every day Sanders delays the party’s healing is a contribution-in-kind to Trump.

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