Even President Trump's base has not been impressed with his performance lately.

Just 38 percent of voters approve of how Trump handles his job, a Quinnipiac University poll published Tuesday found. Among white voters without a college degree, who largely voted for Trump in 2016, 49 percent said they approved and 47 disapproved. While that approval rate is high compared to most other demographic groups, it's a significant drop from just last month, when the same group of voters approved of Trump's performance 57-36 percent.

The poll gives some hint of what may have caused the sudden drop: Most voters said Trump's summit with Russian President Vladimir Putin was a failure for the U.S., and a wide majority said it was a success for Russia. More than half — 54 percent of voters overall — say Trump was not acting in the "best interest" of the U.S., and 48 percent of white voters without college degrees agreed. The summit with Putin, combined with Trump's aggression toward NATO allies and the ongoing investigation into whether his campaign colluded with Russian interference in the 2016 election, have given Trump his lowest approval ratings since February.

Republicans overall still say they approve of the president, as do white evangelical Christian voters. But white men, who last month approved by a margin of 12 percentage points, are currently divided, with 49 percent approving and 47 percent disapproving.

The Quinnipiac poll was conducted July 18-23, surveying 1,177 voters reached by phone. There is a margin of error of 3.5 percentage points. See more results at Quinnipiac. Summer Meza