This chart represents the results of a CBS News / YouGov Poll done between August 10th and 16th. They questioned 4,989 voters in the 57 most competitive congressional districts in the country. The margin of error is only 1.8 points.
The question asked was whether the voter would vote for a congressional candidate that did not agree with their own view of Donald Trump (whether that is positive or negative). About two-thirds (65%) said the candidate MUST agree with them about Trump, while only 35% said they didn't have to agree with them. And every single demographic group had a significant majority saying the congressional candidate must agree about Trump.
That tells me this election really is a referendum on Donald Trump -- and that's not good news for Republicans. Trump remains a deeply unpopular president.