There's two levels to this - establishment and base

[el_bryanto]

For the base I think it really is a matter of they believe what trump tells them, and will not believe anything that contradicts what their leader tells them. They have practiced for decades dismissing anything that isn't what they already believe as fake news.

For the elites it's more a matter of political calculus. Whatever they think of Trump, they know that they are more likely to get stuff out of him and his presidency than they are out of a Democrat.

Bryant