Image credit: Jacquelyn Martin/AP Photo

Hillary Clinton sits at the top of the pack in a new poll of Iowa voters, but her closest competition is firebrand Republican Sen. Rand Paul of Kentucky, a new poll found.

Clinton would beat rising-star Sen. Marco Rubio, R-Fla., handily, 48 to 37 percent, according to a new Quinnipiac University poll released today. But Paul trails her by only 4 points.

Paul, 50, traveled to Iowa earlier this month, stoking speculation that he is courting voters for a 2016 run. Incidentally, around the same time he pointedly jabbed Clinton saying that her involvement in the aftermath of the attacks on the U.S. Consulate in Benghazi, Libya, last year made her unfit for "high office."

Iowa voters have the distinction of being the first to weigh in on the presidential election every four years at the Iowa caucuses. And the swing state's 6 electoral votes are often key to reaching the 270 votes needed to win the presidency.

Quinnipiac pollsters believe that Paul's swing-state travels might be working with voters.

"In general, Senator Paul appears to be the better GOP candidate at this point in Iowa," Peter A. Brown, assistant director of the Quinnipiac University Polling Institute, said. "Part of the reason may be the publicity from his recent high-profile visit to the state, but more likely is that he begins with a solid base of support, the folks who voted for his father [former Texas Rep. Ron Paul] in the 2008 and 2012 caucuses."

In a state where President Obama's approval rating is upside down, Iowa voters are also hesitant to back his vice president Joe Biden, who has intimated an openness to another presidential run.

If the election were held today, Biden would lose to Paul 44 to 39 percent. And he trails Rubio by a single point, within the poll's 2.6 percent margin of error.

Obama won Iowa independents last year by 14 points, but Biden is losing at the moment to both Paul and Rubio among independent voters.