White Christians support for President Donald Trump has slipped since August, a new Pew Research Center survey has found.

Overall, Trump is still the favored pick for president among white Christian voters, with majorities of white evangelicals, white Catholics and white non-evangelical Protestants telling Pew they were leaning toward voting for him. But since white Christians are a key part of the electorate making up about 44% of registered voters the smallest dip in support in a few crucial swing states could spell trouble for Trump.

The dip was particularly noticeable among white Catholics, according to data published Tuesday. In late July and early August, Trump held a 19 percentage point lead on the Democratic nominee, former Vice President Joe Biden , who is Catholic (59% to 40%). That lead shrank to just 8 points in Pews latest poll, which was conducted among 10,543 registered voters nationwide from Sept. 30 through Oct. 5.

White non-evangelical Protestants support for Trump dropped from 59% over the summer to 53% this fall.

The presidents most reliable supporters white evangelical Protestants are still firmly in his camp, with 78% saying they intended to vote for Trump next month. But even in this group, a few percentage points had been shaved off since the summer, when 83% said they would vote for Trump.