‘If 2006 and 2010 patterns hold, a Democratic midterm wave could appear late in the day as vulnerable GOP House seats become targets.
…A lot of seats that wound up falling weren’t even on the radar a few months earlier. Right now, Cook has 34 Republican-held House seats looking very vulnerable (3 are likely Democratic, 7 lean Democratic, and 24 are toss-ups). But the landscape could get much bluer in a hurry.
What would account for this kind of late trend? In 2006 and 2010 it was not, interestingly enough, any deterioration of the president’s own approval ratings. So Donald Trump’s exceptionally stable approval ratings won’t necessarily serve to limit his party’s losses in the House. Late trends could also reflect intensifying excitement over an approaching win for the “out” party…’