At long last, Special Counsel Robert Mueller has submitted his report to the attorney general. What does that mean for Congress — and the question of impeachment? For 21 months, leaders of both parties have found one consistent area of agreement: the ongoing Mueller investigation provided a convenient excuse to duck, deflect, and delay discussion of impeachment. With each new revelation of impeachable conduct, the bipartisan response from Congress has been that impeachment talk was “premature” until the Mueller report was complete. That excuse is now gone. The question is whether the House of Representatives will begin an impeachment investigation,...