is just an established fact. If Howard Dean took him seriously, he could have endorsed him. If Pat Leahy took him seriously, he could have endorsed him. If Liz Warren took him seriously, she could have endorsed him. The people who knew Bernie best ignored him the same way they'd ignored Dennis Kucinich in past races.

More important, did Bernie really WANT Pat Leahy and Howard Dean's endorsements?

This is what Bernie was running on! This (the fact that nobody took him seriously) is how he was able to present himself as a revolutionary even though he was a career politician and a sitting US Senator. He wasn't trying to run on his record, he wasn't trying to run on all the bills he'd had signed into law. He ran as a revolutionary (and, for whatever reason, he still hasn't drummed up a revolution, or even an electoral coalition).

As for whether she'd support him, come on. Of course she'd support him if he was the nominee. I doubt he'd want her to be making any appearances. But she'd be at his disposal as Democrats always are for the nominee. She's just being coy right now to remind whatever adults remain in the party that he doesn't deserve to be taken seriously as a candidate now, just like he didn't deserve it then.