The whole Dem argument for what they hope leads to impeachment is "Trump thought some bad things."
I'm not lawyer, but I don't think we're at the moment in our nation's history where people can be charged, convicted, and thrown into prison for thinking about doing something.
They're trying to get Trump on obstruction, but he basically ended up not obstructing anything. He could have fired Mueller and done other things. But he didn't do them.
At the end of the day, he let the proceedings go on while grousing about the process. Again, there is no law that says you can't complain when some people are trying to railroad you in a kangaroo court.