The congressional generic ballot continues to drift slowly in the Democrats’ direction. But there’s been some tightening in key Senate races that have looked promising for Democrats. These are all very small shifts that are as likely to be noise as actual trends. But the fact that most of these small moves are in the GOP direction suggests it’s something more than noise. The simplest explanation is that a variety of factors allowed Democrats to dominate the airwaves through the late summer. Republicans had fundraising challenges; they hadn’t settled yet on nominees; their various committees and mega-donors were feuding among themselves. That’s changed now. And that change seems to be showing up in the polls.