Andrew Cuomo has a credibility problem.

He wants the city of New York to pitch in more for the MTA capital program, but Bill de Blasio doesn’t trust him with the city’s money. Why should he, when Cuomo has a well-documented habit of diverting dedicated MTA funds to cover other state obligations.

De Blasio has been asking the governor to guarantee that the raids will stop as a condition for a greater city contribution to the capital program. As a ground rule for negotiation, it’s hard to argue with. If someone asked you for a few billion dollars, wouldn’t you want some assurances that it would be spent on the stuff you agreed to pay for — and not stuff like this?

Cuomo’s response yesterday was to mock the very notion that he’d raided the MTA. The annual $20 million diversion that the governor set up for every year from 2014 to 2031? Calling attention to that is “a joke,” Cuomo says.

Okay, then it still seems there’s an easy way to fix this impasse. All the governor has to do is promise not to divert MTA funds again. Just sign a piece of paper that says the state agrees not to siphon off any dedicated transit funds again.

If $20 million is so insignificant, what’s so hard about that?