CNN

Romney's state campaign manager said Monday that a new poll might be a bit optimistic.

COLUMBIA, South Carolina (CNN) – The South Carolina campaign manager for former Massachusetts governor Mitt Romney is downplaying a new state poll from American Research Group that shows Romney leading the competition among likely Republican voters.

"As much as I would love to say that Governor Romney is clearly winning at 26 percent, the fact of the matter is that (as I’ve been saying all summer) polls this early are difficult to rely on," Romney's South Carolina campaign manager Terry Sullivan wrote in a memo sent to supporters Monday.

The ARG poll showed Romney surging from 9 percent to 26 percent in the last month, with former New York City Mayor Rudy Giuliani at 23 percent, Sen. John McCain at 15 and former Sen. Fred Thompson of Tennessee at 10 percent. Thirteen percent of the voters were undecided. The margin of error was plus or minus 4 percentage points, putting Romney and Giuliani in a statistical dead heat.

"It's still early, so I fully expect that we’ll see numbers come out in the next month that have Governor Romney well below the 26 percent that the ARG poll shows," Sullivan's memo said. "As I said above, hard numbers from polls are notoriously difficult to rely on this far out from the election."

In most South Carolina polls, Romney comes in around 10 percent, putting him in fourth place behind former New York City mayor Rudy Giuliani, former Tennessee Sen. Fred Thompson, and Arizona Sen. John McCain. Romney is the only GOP candidate running television ads in South Carolina, which could explain his sudden reversal of fortune.

Despite his skepticism, Sullivan used the poll to say that Romney has momentum.

"As you can see above, Governor Romney is the only candidate that is displaying a clear upwards trend – each of the other candidates is either falling or plateauing, depending on the survey," he wrote.

– CNN South Carolina Producer Peter Hamby