(AP Photo/Craig Ruttle)

On MSNBC today, Bernie Sanders once again declined to endorse Hillary Clinton, and did not signal any particular urgency, or even any timeline, for doing so. He stuck to his ongoing claim that his focus right now is to make the Democratic Party platform as progressive as possible.

Will Sanders’s top supporters in the Democratic Party be able to abide that position for much longer?

In an interview with me this afternoon, Dem Rep. Raul Grijalva — the co-chair of the Congressional Progressive Caucus and one of Sanders’s most important supporters in Congress — said that Sanders should endorse Clinton before the convention, and suggested that the failure to do so could make the job of defeating Donald Trump harder.

“It’s got to happen prior to the convention,” Grijalva told me. “It would make coalescing to defeat Donald Trump easier. It makes the process of unifying to defeat Trump and elect Hillary smoother.” At the convention, Grijalva added, there should be no uncertainty about Sanders’s position, so that the topic can be all about “defeating Donald Trump and the content of the platform.”

Grijalva allowed that, by not rushing, Sanders might be trying to gently coax along his supporters to ultimately get behind Clinton, and noted that he understood Sanders’s goal is to improve the platform. But Grijalva added that the first draft of the platform, which was unveiled last weekend and included concessions to Sanders — such as commitments to a $15-per-hour minimum wage, breaking up too-big-to-fail institutions, and expanding Social Security — already represented substantial movement in his direction.

“I think the movement towards a $15 minimum wage is a victory,” Grijalva said. “I think the platform will reflect many of the things that we want.”

That would be no small thing. As Jeff Stein explains, the platform represents a “blueprint for where the party is headed” and articulates “the clearest expression of what the party stands for.” And it already looks like it will bear Sanders’s stamp in a big way.

But Sanders is still not revealing his intentions towards Clinton. Sanders had previously said he will vote for Clinton, but today on MSNBC, Andrea Mitchell pressed Sanders on whether this constituted an endorsement of Clinton, and Sanders said it didn’t: “They’re not one and the same.” Sanders added that he was “trying to see that we have a Democratic platform that represents working families.”

Sanders did also praise the compromises reached on the platform so far. But, by linking his endorsement to questions about the platform’s future, Sanders left no doubt that he is holding off on endorsing Clinton right now for the express purpose of wringing more concessions out of the process to make the final platform more progressive. Sanders added that he wanted to see language in it opposing a Congressional vote on the Trans-Pacific Partnership trade deal in this session, and noted that talks are ongoing with the Clinton campaign.

Yet it’s unclear whether withholding that endorsement of Clinton makes it more likely that Sanders will win the concessions he seeks. The next step is for the current platform draft to go to the convention’s full Platform Committee, which is made up of 187 members from across the country, including 25 picked by the DNC, with the remainder picked by each campaign in numbers proportional to  the final pledged delegate count from the voting in the primaries and caucuses. They will hash out the final platform, with input from the campaigns.

Sanders can and should push for all he is able to get. But that outcome — which will be determined by scores and scores of people via an agreed-upon process — is unlikely to be dramatically influenced either way by whether or not Sanders endorses Clinton in the interim. Meanwhile, events are moving on without Sanders: Elizabeth Warren is increasingly filling the space he might have filled, and while the Clinton team surely wants Sanders’s endorsement, his voters are gravitating towards Clinton even without his prompting.

Regardless, it remains unclear how Sanders will proceed. Harry Jaffe, a journalist who wrote a biography of Sanders called “Why Bernie Sanders Matters,” tells me that Sanders, an independent, has long harbored a genuine distrust of the Democratic Party that may be tough for him to overcome now.

“Bernie has two problems,” Jaffe says. “He’s told his followers that Clinton is one of the Wall Street evil ones. He’s a true believer in his own rhetoric that the Democratic Party represents the establishment. How can he turn around and endorse the ‘enemy’ of his people?”

If not, the question becomes whether his top supporters in the Democratic Party can stand by for much longer.