TRENTON — Gov. Chris Christie is tied for second-to-last among nine potential Republican presidential candidates in a new poll of Iowa voters that has 2012 presidential nominee Mitt Romney leading the pack.

The poll by Gravis Marketing shows Romney enjoying a 21 percent share of the Republican Iowa caucus vote, followed by former Florida Gov. Jeb Bush at 14 percent and Wisconsin Gov. Scott Walker at 10 percent. Christie tied for eighth place with U.S. Rep. Paul Ryan of Wisconsin, at 5 percent. U.S. Sen. Marco Rubio of Florida was last, at 4 percent.

The first-in-the-nation Iowa caucuses are still a year away, which is likely why the second highest response (18 percent) was "undecided." But the news is not good for Christie, who invested a significant amount of time in the state over the last year as chairman of the Republican Governors Association, making four trips to the state in the run-up to the mid-term elections, three of them last October.

Christie also vetoed legislation banning the use of pig gestation crates in New Jersey in late November, unleashing a barrage criticism that made him fodder for late night talk show hosts like Jon Stewart, but drawing praise from Iowa Gov. Terry Branstad. Although there are fewer than 9,000 pigs in the Garden State, there are over 20 million in Iowa, where nearly a third of the nation's hogs are raised, and where hog farming contributes some $7.5 billion to the state's economy.

Experts have been urging Christie to declare his intention to run soon, or risk being edged out by Romney and Bush.

Later this month, Christie will attend the "Iowa Freedom Summit," co-hosted by U.S. Rep. Steve King (R-Iowa) and Citizens United, along with other 2016 GOP hopefuls like Walker, former Arkansas Gov. Mike Huckabee and current Texas Gov. Rick Perry.

The Townhall/Gravis poll of 404 registered Republican voters was conducted from Jan. 5-7 using interactive voice response technology and "weighted by historical voting demographics" according to the pollsters. The poll carries an error rate of 3 percent.

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Claude Brodesser-Akner may be reached at cbrodesser@njadvancemedia.com. Follow him on Twitter @claudebrodesser. Find NJ.com Politics on Facebook.