"The impulse may be to just move on impeachment right away, but I think we have to explore those 10 areas that the Mueller report left open-ended relative to whether or not the president committed obstruction of justice," Higgins said at the time.

Higgins said he reversed course on an impeachment inquiry after witnessing what he sees as an 11th possible obstruction of justice: Trump's refusal to provide information and produce witnesses in response to subpoenas issued by House committees investigating the administration.

"An impeachment inquiry strengthens Congress's hand in seeking information and witnesses to fully carry out its responsibility" of overseeing the administration's actions, Higgins said.

Higgins stressed that he's not saying at this point that Trump ought to be impeached.

"You don't know where (the investigation) is going to lead," he said.

Still, he said an impeachment inquiry is needed to allow the House to dig deeper than Mueller did.

"Obstruction of justice is a federal crime," and the Mueller report indicated again and again that Trump attempted to do just that, Higgins said.