At the start of June, many polls showed the emergence of a rare consensus around calls for racial justice and changes to policing, with a majority of Republicans joining other Americans in saying that racial discrimination is a big issue for the country.

But a Monmouth University survey released on Wednesday found that at the end of last month, just 40 percent of Republicans still said racism was a big problem, a drop of 15 percentage points from four weeks earlier.

And while close to four in 10 Republicans told Monmouth researchers at the start of last month that protesters’ anger was justified, that number fell by more than half in the new poll, with just 15 percent of Republicans saying so. A majority of Democrats and independents continued to say that the demonstrators’ grievances were fully justified.