President Donald Trump's approval with American voters has slipped in recent weeks, including among key groups that helped to fuel his electoral win last year, according to a Quinnipiac University poll released Wednesday.

Only 36 percent of voters approved of how Trump is handling the presidency, while 58 percent disapproved. That compares to 40 percent approval and 56 percent disapproval in an April 19 survey.

The poll was conducted from Thursday to Tuesday, meaning most, if not all, of the voters responded before Trump fired FBI Director James Comey.

Support for the president also sagged in three key groups:

Only 29 percent of independent voters approved of Trump's performance, while 63 percent disapproved, compared to 38 percent and 56 percent, respectively, in the April poll.

White voters with no college degree narrowly approved of Trump by a 47 percent to 46 percent margin, compared to a 57 percent to 38 percent split last month.

White men also narrowly approved of Trump, 48 percent to 46 percent, after they approved of him by a 53 percent to 41 percent margin in April.

Still, 82 percent of Republicans surveyed approved of Trump, compared to 13 percent who disapproved.

The poll of 1,078 voters nationwide has a margin of error of plus-or-minus 3 percentage points.

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