And the Czechs have a good intel service.
There are many ways that Mueller might have proof.
And if this is true - if indeed Cohen went to meet with a set of Russians after Manafort was fired - and lied about it - then that’s the ballgame.
Collusion, QED.
Trumpies will have to start arguing that “OK, they colluded with Russian intel, but it didn’t mke any difference! Stop distracting us. GDP growth is up half a point!”
But don’t worry. They’ll be able to do it.