Despite the fact that Bernie Sanders has pulled even with Hillary Clinton in national polls, he went down to a 58 percent to 42 percent defeat in the New York primary. With Clinton's extant delegate lead, the arithmetic is looking very tough for Sanders to be able to win the primary outright.

This naturally leads to speculation about what Sanders might do to leverage his following, should he indeed lose. Democratic Party partisans naturally want him to fall in line behind Clinton, and become little more than a cheerleader.

But this would be foolish. Absent some concessions, there is no reason for Sanders to trust that the Democratic Party would actually work to implement his goals, even partially. He would be wise to extract some concessions before granting his support.

It is of course true that any Republican candidate would be a far worse president than either Sanders or Clinton. But it is also the case that the Democratic Party is not particularly interested in Sanders' social-democratic agenda. When they had gigantic majorities in 2009-10, they only just barely managed to pass a milquetoast health care reform and a too-small stimulus. Their plan to help underwater homeowners was an abysmal failure. They failed to get through a climate bill. They didn't make D.C. a state, or pass paid leave, or sick leave, or drug policy reform, or free college, or a financial transactions tax, or a dozen other things.

There were various procedural obstacles to this, but that's just another way of saying the Democrats didn't particularly care about clearing the institutional clogs (like the filibuster) preventing more quality policy from getting through.

Only very recently has the party begun to halfheartedly and partially disavow the truly wretched products of the Clinton administration, like welfare reform and the 1994 crime bill. They still worship before the false god of deficit reduction. Big cuts to Social Security were just barely avoided by the Lewinsky scandal in the 90s, and sheer Republican intransigence in 2011.

More fundamentally, as David Dayen points out, big-shot Democrats basically believe in the legitimacy of Wall Street, and dislike the steep tax increases that would be necessary to fund a large expansion of the welfare state. (There's also the fact that the actual leader of the party infrastructure is a shill for the payday loan industry.)

Clinton has also run quite a conservative primary campaign, attacking the very idea of social insurance from the right, and pushing for little more than minor little tweaks around the domestic policy edges. She's also been reliably atrocious on foreign policy, refusing to come to grips with the repeated failure of military intervention, and all but promising to put Benjamin Netanyahu in charge of the State Department.

At the end of this primary, lots of Democrats will be suspicious of Clinton, and rightly so. And as the winner of a slew of primaries, Sanders will have a legitimate claim to speak for a huge number of Democratic voters. It's only right and proper that he should get some say in what the party will stand for.

So in return for an endorsement of Clinton, Sanders ought to demand a few big policy commitments — perhaps his trillion-dollar infrastructure plan, a public option for ObamaCare, and a plan for free state college, or some other combination. He should not automatically endorse party insiders in congressional primaries, who are often conservative austerians.

Of course, that doesn't guarantee that the party won't try to forget all about that later. But presidents do generally try to keep their promises, and if he can't win, Sanders will have to try something like this if he wants to push the general election leftwards. He's got a fairly strong hand to play — Clinton's popularity numbers are terrible, and she will likely need Sanders voters if she is going to win by a big enough margin to take the House and Senate. If she wants them, she's going to have to make some leftward compromises for once.