Senator Martha McSally of Arizona, a Republican, trails her Democratic opponent, Mark Kelly, by nine percentage points while Senator Thom Tillis of North Carolina is behind his Democratic rival, Cal Cunningham, by three. Both incumbents are polling below 40 percent despite having recently aired a barrage of television advertisements.
In Michigan, which Senate Republicans viewed as one of their few opportunities to go on the offensive this year, Senator Gary Peters, a first-term Democrat, is up by 10 percentage points over John James, who is one of the G.O.P.’s most prized recruits.
The poll showed that the same voters who are fleeing the president — highly educated white Americans, many of them once-reliable Republicans — are providing an advantage to Democratic Senate candidates. Mr. Trump’s mismanagement of the coronavirus and his bombastic response to protests over racial justice have made him an underdog against Joseph R. Biden Jr., the presumptive Democratic nominee, who led the president by 14 percentage points nationally in the Times poll.