Why is a pro-impeachment majority likely? Because there are plenty of Democrats who have yet to come out for impeachment but who face similar political pressures to those who already have. The 109 Democrats who currently favor impeachment, not surprisingly, mostly represent very liberal districts; on average, Trump lost those districts in 2016 by about 38 percentage points. (Trump lost the average Democratic-held House district by 28 percentage points, and he lost the average district with a member not supporting impeachment yet by 20 points.) Of the 126 Democrats who are not yet on board with impeachment, 29 represent districts where Trump lost by at least 38 points. If just nine of those 29 embraced impeachment, the pro-impeachment wing of House Democrats would have a majority.

Those 29 members, representing such liberal districts, are likely to face some pressure to get on board. Polling suggests that while a majority of Americans oppose impeachment, a clear majority of Democrats favor it. In a congressional district where Trump lost by 38 percentage points, the sentiment is likely to be heavily in favor of impeachment.

It’s not that these House members will necessarily face primary challenges if they don’t join the impeachment push. But with the House now on a six-week recess, it’s likely that many of these members will be asked about impeachment by their constituents in their home districts, and I suspect few of them want to defend Trump’s conduct on the merits.