Who is "they" in this sentence? You mean the Republican majorities in both houses of Congress who (nearly) all have their seats at this point only because they appealed to Trump's mob of followers? He could be impeached for all manner of things, but (as the parent comment said) I don't know what it would take for these Republicans to do it.

When he first took office in 2017, I figured that it would happen within six months. Given that he was impeached twice, I was almost right, but it didn't happen until Democrats won the House. Even most of the "old establishment" Republicans ended up backing him. Now there are none of those remaining.

The DOJ isn’t involved in that so no