As New Hampshire voters chose among GOP candidates in the first-in-the-nation primary on Tuesday, the largest pro-Republican super PAC on issued a strong defense of Mitt Romney’s chances at becoming the Republican presidential nominee.

The communications director for American Crossroads, Jonathan Collegio, wrote in a memo that political pundits and Democratic operatives were pushing a “plainly dumb idea” that Romney’s support is stalled at about 25 percent of the GOP electorate. Instead, Collegio wrote, the approval levels seen in polling for Romney so far are "a floor, not a ceiling."

"With Mitt Romney, as opposed to virtually every other candidate in the GOP field this cycle, the difference is that his negatives (all candidates have them) are already widely known and built into his level of support," Collegio wrote. "...there is very little out there about Romney that Republican voters don’t already know that could significantly affect his support.”

Collegio added, "That may well be an underlying reason why Republicans almost always nominate candidates who have run in previous elections."

The analysis may be more important for what it says about American Crossroads than what it says about the Republican frontrunner, however. Crossroads, which was founded with the help of GOP political guru Karl Rove, is a combination nonprofit group and "super PAC" that plans to raise $240 million in 2012, far more than any other outside group. Until now, it has tried to avoid appearing to take sides among the candidates vying for the Republican nomination.

In a followup note Tuesday, Collegio sought to tamp down any speculation that the group was endorsing Romney. "I probably should have been clearer, as some are reading too much into the memo: American Crossroads is, and remains, neutral in the Republican presidential primary,” he wrote.

American Crossroads was widely viewed as having a pro-Romney tilt even before Collegio's memo, in large part because the PAC’s political director, Carl Forti, helps run a pro-Romney super PAC that spent millions in Iowa targeting the primary campaign of former House speaker Newt Gingrich. 

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Mitt Romney under attack as New Hampshire vote looms

Dana Milbank: Mitt Romney's money problem

The Fix: Is Jon Huntsman a one-state wonder?

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New Hampshire primary: pre-game analysis