But there aren’t yet many signs that the bottom has fallen out for either Mr. Trump or the Republican Senate candidates in key states like Florida, Ohio, Wisconsin, North Carolina, Pennsylvania, New Hampshire, Nevada and Missouri.

Notably, even less popular senators — like Pat Toomey of Pennsylvania and Richard Burr of North Carolina — have held up fairly well in polling this week. On balance, the race looks more or less the way it did a week ago.

The same thing seems to be true in the House. There aren’t many public House polls, but the Cook Political Report updated its race ratings Friday, and there are still just 33 Republicans in either “lean” or “tossup” seats. It’s a very different story from 2006, when the number of competitive House seats quickly surged after revelations that Mark Foley, a Republican congressman, had send lewd messages to a former congressional page.

The Republicans aren’t in the clear quite yet. The biggest warning sign: a big drop-off in the G.O.P.’s standing in the generic congressional ballot. The NBC/WSJ and Fox polls both showed Democrats building six-point leads, up from a one-point lead in the Fox poll and a three-point lead in the NBC/WSJ poll (the prior NBC/WSJ poll was among registered voters).