Support for Sen. Marco RubioMarco RubioCruz wins bulk of delegate spots at Va. convention Trump seeks approval from foreign policy experts, but hits snags Many Republicans uninterested in being Trump’s VP: report MORE's (R-Fla.) potential presidential bid has slipped and Sen. Rand PaulRand PaulFive ways Trump will attack Clinton Carter pledges probe of sex assault testimony Rand Paul wants to legalize cooperation MORE (R-Ky.) leads in the key early-voting state of Iowa, according to a new GOP primary poll conducted by the Democratic firm Public Policy Polling.
Paul, meanwhile, has risen from 10 percent support in February to 18 percent today.
The Florida senator's dip could be driven more by others' rise than his own stature, however.
Rubio's favorable rating stayed unchanged at 54 percent, with a statistically insignificant change from 13 to 14 percent in those who view him unfavorably.
The possible candidates are all very close to one another, however, well within the poll's 6.2 percent margin of error.
Paul is just 2 percentage points ahead of New Jersey Gov. Chris Christie (R), who has 16 percent support.
Former Florida Gov. Jeb Bush (R) pulls 14 percent, Sen. Ted CruzTed CruzObama mocks GOP, media and himself in final WHCD address Obama jabs at GOP: Is this dinner too tacky for the Donald? What Obama said about this year's candidates in past WHCD jokes MORE (R-Texas) is nipping at Rubio's heels at 10 percent support and former Sen. Rick Santorum (R-Pa.), who won Iowa's 2012 presidential caucuses, sits at 6 percent.
This isn't the only recent PPP poll showing Rubio trailing the field of potential candidates, after some polls earlier this year showed him as the front-runner.
PPP's recent poll of Texas Republicans found Rubio in sixth place among candidates, with 6 percent support, and a recent poll of Montana Republicans found him in fifth place.
On the Democratic side, Hillary ClintonHillary Rodham ClintonObama mocks GOP, media and himself in final WHCD address Obama teases Clinton: She's like 'your relative who just signed up for Facebook' What Obama said about this year's candidates in past WHCD jokes MORE dominates her potential primary opponents, with 71 percent support to 12 percent for Vice President Biden and 5 percent for Sen. Elizabeth WarrenElizabeth WarrenWarren: Trump's sexism is as obvious as his 'bad hair' Sanders-Warren ticket would sweep the nation With either Trump or Clinton, average American loses again MORE (D-Mass.). In the general election, Clinton leads all comers by 7 percentage points or more.
PPP's automated poll of 668 voters, including 250 GOP primary voters and 260 Democratic primary voters, was conducted from July 5-7.
The margin of error for the total poll was 3.8 percent, with margins of error of 6.1 percent and 6.2 percent for the Democratic and Republican primary samples.