"Mr Michael Cohen seems to be a main witness. A person with a penchant for lying?"

You need to check that meme bro.

They were Trumpy lies. He lied for Trumpy. Like they all have to do.

Then he manned up and admitted to his lie. Like very few Trumpers can or are willing to do.

Read his books he explains very clearly how he got wrapped up in Trumpy's world of lies and how he finally escaped it.

He had to do time in prison because of Trumpy's lies.

Why shouldn't Trumpy have to do the same for his own lies?

But besides. Everything he says is backed up by other witnesses or documentation.

Trumpy's only way out is to disrupt the trial or tamper with and/or intimidate the witnesses or the jury pool (which he has already done)