I dunno that overpromise/under delivered is right. I think they promised one thing, the public heard a different thing, and then they over delivered on the thing they promised they'd do.
Like deporting undocumented immigrants. They said they were going to deport them. The public heard "get rid of the violent ones but leave the good ones." And then they just started deporting everyone with brown skin and shooting anyone who tried to resist.
But then they promised no new wars, and delivered the exact opposite.
Then they promised to drop prices immediately and prices just went up.
So.. it's more like they promised to make things better and wildly failed.