Some part of that is from Trump himself. He is compelled by some inner voice to respond to every idiotic charge that is leveled against him. He doesn't understand the game, and therefore he fall straight into almost every trap they set.
It is an odd situation when the most powerful thing you can do in a given situation is to do nothing, and keep your mouth shut. I'm not sure Trump is capable of doing either of those things.
And yet every time, Trump has prevailed in the end. Because the Democrats have always been nuttier than he has been. He's drawing them out.