Moreover, likely voters divide essentially evenly, 47-46 percent, between the Democratic and Republican candidates in their congressional district. While the measure’s imperfect (it’s not limited to competitive districts, and doesn’t cover Senate races), it indicates challenges for Clinton forces as they seek to turn her support into a broader, Democratic wave.

Two key reasons emerge for the closer congressional contest in this poll, produced for ABC by Langer Research Associates. One is independent voters; the other, Republicans returning home for their local races:

• Independent likely voters divide evenly between Clinton and Trump, 41-41 percent in the latest tracking data. By contrast, independents favor the Republican over the Democrat in their congressional district by 51-39 percent.

• Trump wins 82 percent of Republicans in the presidential race, ceding 8 percent to Clinton and 6 percent to third-party candidates. In the congressional trial heat, however, 94 percent of Republicans stick with the GOP.