Support for Sen. Marco RubioMarco RubioFla. Senate candidate bashes Rubio The Hill's 12:30 Report Rubio: 'Maybe' would run for Senate seat if 'good friend' wasn't MORE's (R-Fla.) potential presidential bid has slipped and Sen. Rand PaulRand PaulOvernight Energy: Trump outlines 'America First' energy plan in North Dakota Overnight Regulation: GOP slams new Obama education rules Paul blocks chemical safety bill in Senate 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 CruzMcConnell: Trump White House will have ‘constraints’ Cruz holds back support for Trump with eye on abortion Trump takes victory lap over rivals' remarks 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 ClintonAsian, Pacific Islander lawmakers to endorse Clinton Feds fight to prevent Clinton deposition in email case Trump decides he won't debate Bernie Sanders MORE dominates her potential primary opponents, with 71 percent support to 12 percent for Vice President Biden and 5 percent for Sen. Elizabeth WarrenElizabeth WarrenVerizon, striking unions reach agreement in principle What Bernie needs to do right now An all-female ticket? Not in 2016 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.