Trump biographer explains how the House could get the IRS commissioner to hand over Trump's taxes immediately

On Tuesday's edition of CNN's "Anderson Cooper 360," Pulitzer Prize-winning Trump biographer David Cay Johnston revealed a simple tactic House Democrats could employ to force the administration to hand over the president's tax returns, that might be even more effective than their new lawsuit against the Treasury Department and the Internal Revenue Service: put pressure on IRS Commissioner Charles Rettig.

"I'm surprised to some degree that the administration won't comply with the law," said Johnston. "And I think the committee has made two mistakes. One ... they have taken too much time and been too polite. The other is the duty, under federal regulations, falls on the IRS commissioner. And I don't understand why they haven't called him in, ordered him to turn them over, which he will never fail to comply with, because it could cost him his law license in California, and he wants to go back to being a lawyer, representing wealthy people who have been caught cheating on their taxes."

"He could actually lose his law license?" Cooper pressed him.

"Oh, sure. Yeah," said Johnston. "I think he could lose his license over refusing to follow the law."

CNN legal analyst Jeffrey Toobin registered skepticism that the California State Bar would go so far as to revoke Rettig's law license, but agreed with the basic point: The administration's behavior is unprecedented and has no legal basis.

"This is just the most obvious, and frankly, egregious example of the White House and the president himself personally just blowing off congressional oversight," said Toobin. "I mean, you know, see you in court, with the understanding that the clock is running."

Watch below.