Donald Trump's brief flirtation with the lead in Republican primary polls may be over, according to a new poll released Tuesday.

The survey, conducted by the Democratic firm Public Policy Polling, found Trump garnering only 8 percent of potential Republican primary voters, down from 26 percent who said they would support him if he ran in PPP's previous survey. That plunge in support was enough to drop him from a solid first place to a tie for fifth place.

As recently as last week, a CNN poll conducted April 29-May 1 found Trump vying for the lead in the Republican primary with 14 percent to Mike Huckabee's 16 percent. So far, Republican primary surveys have shown that no frontrunner has emerged in the race, which means that candidate rankings in those surveys can be particularly volatile.

To add to the woes, Trump's favorable rating among Republicans is deep in negative territory in the new poll. Previous surveys had found that Americans more generally had an unfavorable opinion of Trump, but showed him with at least tepidly supportive ratings among Republicans.

Trump's drop in support could be related in part to a sharp drop in the number of Republican "birthers," as measured by PPP, since President Obama released his long-form birth certificate to the public. In the new poll, 48 percent of Republicans said they believed Obama was born in the United States and 32 percent said that he was not. In a February PPP poll, the firm's most recent poll on the subject conducted before the birth certificate release, only 28 percent said he was born in the US while a 51 percent majority said that he was not.

On top of that, a CBS/New York Times poll conducted April 15-20, before the birth certificate release, found that even among Republicans, only 37 percent said that Trump was a serious candidate and 57 percent said that he was not.

The new poll was conducted between May 5 and May 8 among 610 "usual" Republican primary voters using automated telephone technology, and has a margin of error of 4 percentage points.