His daily news briefings on the coronavirus outbreak are inflicting grave damage on his political standing, Republicans believe, and his recent remarks about combating the virus with sunlight and disinfectant were a breaking point for a number of senior party officials…

Republicans were taken aback this past week by the results of a 17-state survey commissioned by the Republican National Committee. It found the president struggling in the Electoral College battlegrounds and likely to lose without signs of an economic rebound this fall, according to a party strategist outside the R.N.C. who is familiar with the poll’s results.

The Trump campaign’s own surveys have also shown an erosion of support, according to four people familiar with the data, as the coronavirus remains the No. 1 issue worrying voters.