President Trump’s support has eroded among key groups of voters who backed him in 2016 — a major reason why he continues to trail former Vice President Joe Biden and a prime motivator for the president’s reelection strategy of emphasizing violent disorder in the nation’s cities.

Trump’s decline among parts of his 2016 base is a chief finding so far from the USC Dornsife Daybreak Poll, which tracked voter preferences daily four years ago and is doing so again this year. Overall, Trump has lost support from about 9% of voters who backed him in 2016, the poll finds.

The poll shows no major shift in the race during the last two weeks, belying much speculation that the back-to-back national political conventions and violence in Portland, Ore., and Kenosha, Wis., might have changed what has been an unusually stable contest.