Bernie Sanders is playing a selfish, dangerous game.

He has no chance of winning the Democratic nomination -- none, zero, zilch. Yet he persists in attacking Hillary Clinton, and his supporters threaten to disrupt the Democratic convention in a way that can have only one effect: helping elect Donald Trump president.

Does he want that to be his legacy? Apparently he doesn't care. Sanders' ego has swelled to Trumpian proportions, and he has rejected numerous and increasingly desperate appeals from senior Democrats to recognize reality and back off.

Sanders and his wife, Jane, we are told, feel "disrespected" by party leaders and have somehow decided that Clinton and the Democrats are his real enemy, not Trump and the Republicans.

The New York Times reported recently that his strategy was "aimed at inflicting a heavy blow on Hillary Clinton" before the end of the primaries. Even if Sanders doesn't win the nomination, he would "arrive at the Philadelphia convention with maximum political power."

Tad Devine, a senior Sanders strategist, told the Times that the candidate was "not thinking about" the damage he was inflicting on Clinton. "The only thing that matters is what happens between now and June 14," he said. "We have to put the blinders on."

Exactly. "Blinders" is the right word. Team Sanders is so consumed by its own self-righteousness that it has become one of Trump's top assets. And Republicans are ecstatic.

"Just to acknowledge the obvious," veteran GOP strategist Ed Rogers wrote in The Washington Post, "Clinton and the Democratic ticket become weaker the longer Sanders stays in the race."

Trump himself understands how useful Sanders has become, taunting in a tweet that "Bernie Sanders is being treated very badly by the Democrats -- the system is rigged against him. Many of his disenfranchised fans are for me!"

In the latest NBC/Wall Street Journal survey, Clinton's favorable rating among Democrats has dropped from 84 percent last June to 65 percent; her negatives have jumped from 7 percent to 21 percent. Just 66 percent of Sanders supporters say they will back Clinton against Trump.

Sure, Clinton's missteps have aggravated her problems; and sure, those numbers will change once she's nominated. But Sanders is not losing gracefully. He is planting seeds of long-term grievance, particularly among younger voters, calling Clinton the "lesser of two evils" and arguing that somehow "the system is rigged" and she is stealing the nomination unfairly.

That is false. Sanders claims to be a pillar of integrity, but he's deceiving his supporters. Clinton has won fair and square. She has 3 million more votes and 271 more elected delegates -- 766 more, when superdelegates are included.

Sanders has been deeply deceitful in another way as well. He has promised his followers a leftist "revolution" that was never, ever going to happen. He set them up for the bitterness and disappointment that is now infecting their ranks.

He is the liberal version of the tea party, which told conservatives that if they were sent to Washington, they would change the basic nature of the capital, repealing Obamacare, curtailing abortion and heralding a new conservative era.

That was a lie from the beginning. With a Democrat in the White House, the tea party agenda stood no chance of ever being achieved. But the resulting frustration in Republican circles helped drive Speaker John Boehner and his chief deputy Eric Cantor into premature retirement.

Sanders is fomenting the same kind of frustration among his supporters. They have been promised a Fantasy Land of liberal proposals that stand no chance of passage -- none -- in modern America.

This is a center-right country. In 2012 exit polls, only 25 percent of voters identified as liberals (35 percent identified as conservatives, and 41 percent as moderates). Ted Cruz was flat-out wrong to say that Republicans have failed to win the White House because their candidates were not conservative enough. And Sanders is just as misguided to say that what the Democrats need is a more purist liberal as their standard bearer.

Sanders' animosity toward Clinton would not matter so much if she were running against an extreme conservative like Cruz, or even a conventional Republican like Mitt Romney. Geography and demography heavily favor the Democrats, who have won the popular vote in five of the last six presidential elections.

But Clinton is running against Trump. Trump is different. Trump is unpredictable. Trump can shuffle the deck and scramble expectations.

And Sanders is helping him.