Josh Marshall on the reaction to the impeachment

We've been pushing this for a long time, but political journalists (at least the smarter ones like Marshall) are getting better about thinking through the implications of selection effects on polling data.

Why Are President Trump’s Poll Numbers Going Up?

But there is another plausible explanation. Pollsters call it differential response. When one side gets enthused or energized their numbers go up but in an ephemeral fashion. The pumped-up side is a bit more eager to answer the phone or fill out the survey. The demoralized side is a bit less eager. This is a real and demonstrated phenomenon, not just a concept or speculation. It’s not necessarily an error per se in the polling. It’s picking up something real. It’s just ephemeral.

One example many of us likely remember came after the first general election debate in 2012. President Obama turned in a stiff and disconcertingly flat performance. The consensus was that Mitt Romney won the debate and for the first and last time in the cycle Romney briefly pushed into the lead.

There are good reasons to think that at least some of that is happening today — the President’s impending acquittal and Republican unity have been the driving news of the last two or three weeks. Republicans are energized and enthused by the certainty of President Trump’s acquittal. Many Democrats are demoralized by seeing an overwhelming and exacting case made for the President’s guilt and seeing it simply not matter.