Mueller has made life much tougher for Democrats from districts where Trump is popular. They’ve been walking a tightrope: To avoid offending progressives, they agree that the president has committed impeachable offenses; to avoid offending Trump-sympathetic constituents, they argue that there is no point proceeding with impeachment because there is no way the GOP-controlled Senate would remove the president.

To pull this off, they’ve been relying on the seeming ambiguity of Mueller’s treatment of the obstruction question: Was he saying there was not enough evidence, or was he saying the OLC guidance prevented him from charging? Today, he indicated it was the latter — and, for good measure, he added that in our system it is for Congress to take action against a sitting president. From that premise, the hardline anti-Trump Left will now argue that if Congress does not act, it is shirking its duty and placing the president above the law.

That is why, after Mueller finished speaking, a number of Democrats vying for the 2020 presidential nomination stridently called for impeachment. They are trying to appeal to the anti-Trump base of the party and distinguish themselves from the so-far-cautious front-runner Joe Biden. Expect lots more of this. It’s going to put a lot of pressure on Democrats who quietly believe that impeachment is a political loser.