The thing about Cohen that puts me off is that the campaign finance violation he is pleading guilty to is extremely weak. If you go by precedent, the chances he would be found guilty in a court of law is almost zero. He could easily make the case that paying hush money to protect his client's image is a regular thing with Trump, and I doubt anyone would argue with that.
So why would he plead guilty and walk into a jail cell without a fight?
Probably because they have some much more serious dirt on him. A much more serious case with a much worse punishment, should they decide to prosecute him. But it must not be something that implicates Trump, otherwise they would just go with that. So instead they offer Cohen a deal, where he pleads guilty to campaign finance violations, since that will also make Trump look guilty even though it's unlikely he will be charged with anything, since the evidence is so weak.
And now we have Cohen going before congress to fulfill his plea deal by making accusations against Trump, to make him look guilty of stuff, but without providing any evidence of anything, which will result in nothing but an attack on Trump's image, which seems to be the entire point of this circus from day 1.