New Jersey Gov. Chris Christie has edged ahead of former Secretary of State Hillary Clinton in a new Iowa poll, 45 percent to 40 percent in a head-to-head matchup.

The latest survey by Quinnipiac University shows that Christie, a Republican, has improved in the hypothetical contest against Clinton, a Democrat, since this summer, when another Quinnipiac poll showed them tied at 41 percent. Some of that recent boost is likely from Republicans in general gaining ground amid the rocky Obamacare rollout.

Clinton comes out on top, however, in matchups against other potential 2016 Republican presidential contenders -- Sens. Rand Paul of Kentucky and Ted Cruz of Texas, and former Florida Gov. Jeb Bush.

The poll shows that Iowa voters believe either Christie or Clinton would be a good president. They are less certain of Paul, Cruz and Bush, who the preponderance said would not make a good president.

The one potential candidate that Iowa voters say is least likely to make a good president is the man who has been closer to the Oval Office than any other: Vice President Joe Biden, a Democrat. Sixty-two percent of Iowans don't think Biden would be a good president.

Running second-worst to Biden is Cruz, who became a highly divisive figure during a budget fight that led to a government shutdown. Forty-two percent said Cruz would not make a good president. Another 28 percent said Cruz would make a good president, while 30 percent did not have an opinion.

Most Democrats think Biden would not run for president if Clinton runs, but he made his first trip to Iowa this year to headline Democratic Sen. Tom Harkin's annual steak fry, a high-profile political event.