There were lots of accusations flying and a lot of name-calling last week when President Donald Trump’s former attorney and fixer-in-chief Michael Cohen testified before the Congress House Oversight Committee.

Cohen called Trump a liar. He said Trump was deeply involved in hush payments to cover-up sexual misconduct. He said Trump lied about business interests and lied to reporters about stolen Democratic emails.

Republicans on the committee asked why Cohen should be believed. But what has C...