Support for Sen. Marco RubioMarco RubioFlorida: 'High likelihood' of first Zika transmission in the US Overnight Healthcare: Rubio presses Obama to spend Zika money | FDA moves ahead with trans fat ban The Trail 2016: Her big night MORE's (R-Fla.) potential presidential bid has slipped and Sen. Rand PaulRand PaulGreen party candidate: People have 'real questions' about vaccines What to watch for on Day 2 at the GOP convention Cyber squatters sitting on valuable VP web addresses 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 CruzHot air balloon crash kills 16 in Texas 100 days to go in volatile race Voting Trump because of the Supreme Court isn't enough 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 ClintonTrump: Muslim soldier was a hero but his father 'has no right' to criticize me Interim DNC chair to impose 'tough standards' after email leaks Mark Cuban campaigns for Clinton in hometown of Pittsburgh MORE dominates her potential primary opponents, with 71 percent support to 12 percent for Vice President Biden and 5 percent for Sen. Elizabeth WarrenElizabeth WarrenWasserman Schultz: 'Sometimes you just have to take one for the team' Chelsea Clinton's big moment Kaine as Clinton's VP pick sells out progressive wing of party 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.