Three hours later, Sanders appeared on MSNBC's "Up With Chris Hayes" and explained, for the umpteenth time, that his promise to help defeat Donald Trump and vote for Clinton did not amount to an endorsement. Not yet.
"I talked to Joe, I think, was three weeks ago," said Sanders, referring to a much-watched meeting between the two men at the vice presidential residence. "Look, on that issue, we are trying to work with Secretary Clinton's campaign on areas that we can agree on."
Hayes followed up twice, attempting to get more than boilerplate from the Vermont senator.
"Is it just the case that you are never going to be in enough policy agreement with Hillary Clinton that you will never be in that position?" he asked.
"Let me back it up by saying that I'm going to do everything I can to defeat Donald Trump," said Sanders, going on to promote his fight to add free public college tuition, universal health care, and other progressive goals to the Democratic platform.
"What if 'everything I can' means going to rallies and doing the kind of thing that's standard with campaigns?" asked Hayes.
Sanders gave another version of his stock answer, with a twist, imagining a day when he could tell his voters that Clinton had been brought around.
"We are working with the Clinton campaign, trying to be able to come forward to my supporters and say: You know what, here's the progress we have made," said Sanders. "Here's what Secretary Clinton is saying on this issue and that issue."
Sanders also laughed when Hayes showed him a clip of Trump insisting that the senator secretly despised Clinton and wanted her to lose.
"I do not hate Secretary Clinton," said Sanders. "We have disagreements on issues, but to say that I hate her is absolutely untrue."