Rubio slips, Paul leads in Iowa presidential poll

Support for Sen. Marco RubioMarco RubioRubio: GOP Congress could go in different direction than Trump Poll: Clinton holds 4-point lead in Florida Republicans, it's time to stop asking 'What would Reagan do?' MORE's (R-Fla.) potential presidential bid has slipped and Sen. Rand PaulRand PaulWhat the 'Bernie Sanders wing of the GOP' can teach Congress GOP senators avoid Trump questions on rigged election How low is the bar for presidential candidates, anyway? 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.

Rubio's support has slipped to 11 percent, down from the 16 percent support he had when PPP last polled the state in February. The result come as Rubio fends off conservative criticism for his strong support of a bipartisan immigration bill in the Senate. 

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 CruzIs Georgia turning blue? Five takeaways from money race Club for Growth: Anti-Trump spending proved to be 'good call' 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 outlines first 100 days WATCH LIVE: Trump speaks at Va. rally Trump threatens to sue women accusing him MORE dominates her potential primary opponents, with 71 percent support to 12 percent for Vice President Biden and 5 percent for Sen. Elizabeth WarrenElizabeth WarrenSchilling lashes out: 'I'm apparently an anti-Semite' for asking questions Curt Schilling to Jake Tapper: How can Jews be Democrats? Small donors aren’t revolutionizing Congress. At least not yet. 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.