Incumbency is such a massive advantage that willingly throwing it away, especially when the stakes are as incredibly high as they are right now, is absolutely something that can be legitimately criticized.

And let's not pretend that this is some altruistic act. He'll get on some talk shows, publish a book, and run for a Senate seat when one opens up. Maybe he genuinely believes his own bullshit, but it's hard to not imagine that, on some level, he knows what he's doing here.