I think Donald Trump frightens most Americans. They are worried about his constant lying, his attacks on the press, his inability to get along with our best allies, his weak stance toward Russia (and the attacks they have made on our democracy), his preference for corporations over people, and his threats of war against some other countries. And it has become obvious in the past few months that the Republican Congress will not rein in Trump. They are too busy trying to protect him.
That's why the public now prefers the 116th Congress, which will be determined by the November elections, be controlled by Democrats. They want a check on the worst impulses of Donald Trump, and they think they only way to get that is to elect more Democrats.
The public now prefers a Democrat-controlled Congress by a 10 point margin (50% to 40%). The Republicans are hoping to narrow (or eliminate) that margin before November. I don't think they'll be able to do that. In fact, it may grow even larger.
The chart above uses information in a new NBC News / Wall Street Journal Poll -- done between March 10th and 14th of a random national sample of 1,100 adults, with a margin of error of 2.95 points.