Law professor Jonathan Turley said the record against President Trump is "one of the thinnest records ever to go forward on impeachment."
The only other record that could be as thin as the one against Trump is the record against President Andrew Johnson, he said.
"But this is certainly the thinnest of the modern record. If you take a look at the size of the record of Clinton and Nixon, they were massive in comparison to this, which is almost wafer thin in comparison," Turley said.
The record against Trump, he said, "has left doubts in the minds of people" about what happened.
"There's a difference between requesting investigations and a quid pro quo. You need to stick the landing on the quid pro quo. You need to get the evidence to support it. It might be out there, I don't know. But it's not in this record," Turley said.