Bernie Sanders is making some Democrats very nervous. He has promised to support a primary challenger to Debbie Wasserman Schultz, head of the Democratic National Committee. (Even the threat has Democrats wondering if they should drop her from that role.) He has said that he will take his fight all the way to Democratic convention, vowing that the coronation in Philadelphia will be "messy." Sanders has already appointed Cornel West, who has called Barack Obama a war criminal, as an advisor to his platform committee. And he still tells his supporters that he can win the nomination.

Knowing that absent the sudden death or arrest of Hillary Clinton a Sanders nomination is nearly impossible, liberals are starting to worry that his campaign is going to damage their nominee. When Clinton wants to run on expanding and continuing the increasingly popular administration of Barack Obama, Sanders is elevating Obama haters. By supporting primary challenges in other races, he is dividing Democratic resources. Or Sanders could get his supporters so energized and aggrieved that they refuse to support Clinton, who, by the way, has won many, many more voters than Sanders has. There is some evidence that Clinton's support among younger voters is dropping precipitously.

And there is some fear that Sanders, because he has historically refused to run as a Democrat, has so little loyalty to the party, that he may be willing to hurt its general election chances in a fit of pique. In the grind of a campaign, it hasn't been hard to come across a number of Sanders supporters who are "Bernie or bust" in their politics. The political antagonism with Clinton will make it impossible for them to vote for her in November.

But the fears that Bernie is ruining Clinton's general election campaign are misplaced. In fact, he has most likely done the Democratic Party a favor in this campaign. Clinton, like any mainstream Democrat, was going to have some vulnerability on her left flank. But Sanders has kept left-wing and socialist energy (which is rising, nationally) within the Democratic Party.

Yes, by running as a Democrat, Bernie has had a larger platform from which to criticize Hillary. But he has also given left-wing and socialist politics a larger home in that party. And by running as a Democrat he has prevented a left-wing third party from using the same case and grievances against Clinton to create more ballot access and buzz for a Ralph Nader-like spoiler candidacy.

Just as various campaigns of Ron and Rand Paul led many libertarian activists into the Republican coalition despite deep principled and moral disagreements with the mainstream party, so the Sanders campaign has opened up space in the Democratic coalition. Bernie Sanders is not a threat to Democratic unity unless he promises to take his supporters out of the party into another electoral vehicle, or argues that Donald Trump is better than Hillary Clinton. If he starts comparing Clinton unfavorably to Trump, or he begins saying that Trump has some better policy ideas than Clinton, then he will be a larger problem. But there is no sign that he will do this.

Sanders may cause some platform fights at the convention. He may highlight causes that Clinton doesn't want to talk about, like Palestinian rights or single-payer health care. But he has not taken the fateful step of arguing that she should not be president.

But when Sanders argues for the continuation of his campaign, he cites the importance of defeating Trump, not Clinton. Sanders has consistently focused on the fact that he has high favorable ratings and polls well against the presumptive Republican nominee. He has not done to Clinton what Mitt Romney did to Donald Trump: given a focused anti-Clinton speech that will be the basis for demoralizing ad campaigns in October.

All Sanders has to do is transition from saying that he is the best candidate to beat Trump to saying Clinton bested him for the nomination fair and square and now she is best positioned to defeat the Republican billionaire. That's an easy transition to make. And Bernie will do it.

But in the meantime, for the sake of the causes he believes in and the many supporters who want to vote for him in the final contests, he presses onward.