MANCHESTER, N.H. — At a rally for Mitt Romney in Derry on Saturday morning, Gov. Nikki R. Haley of South Carolina set a high bar for Mr. Romney’s performance in the New Hampshire primary on Tuesday.
“We don’t just need a win in New Hampshire,” Ms. Haley told the crowd while introducing Mr. Romney. “We need a landslide.”
Mr. Romney politely corrected Ms. Haley after taking the microphone, joking that he would be happy to win by twice as large a margin as he did in Iowa last Tuesday. (Mr. Romney was declared the winner in Iowa by eight votes, although the results have not yet been certified.)
Ms. Haley’s confidence is well justified, however. It would require an upset of historic proportions for Mr. Romney to lose New Hampshire.
Although Hillary Rodham Clinton’s defeat of Barack Obama in the 2008 New Hampshire primary was an incredible story, for instance, it would not be in the same ballpark as Ron Paul or another candidate upsetting Mr. Romney. Had we run our forecast model on Saturday, Jan. 5, 2008, it would have put Mrs. Clinton 8.7 points behind Mr. Obama based on the polling at that time and given her a 10 percent chance of defeating him.
By contrast, Mr. Romney’s lead over his nearest competitor, Ron Paul, is 22.6 percentage points based on polling through Saturday morning — more than twice as large as Mr. Obama’s. That’s why FiveThirtyEight’s forecast model gives Mr. Romney just a 1 percent chance of losing.
In fact, were Mr. Paul or another candidate to defeat Mr. Romney, it would be the largest last-minute upset ever in a primary, according to our database, which consists of robustly polled primaries and caucuses since 1980.
The current record for largest upset belongs to Edward M. Kennedy, who would have trailed Jimmy Carter by 21.8 points had we run our forecast model on March 22, 1980, three days in advance of the New York primary.
Another famous upset came in New Hampshire in 1984, when Gary Hart rallied from a deficit of 16.6 percentage points just three days before the primary to defeat Walter Mondale. Mr. Hart beat Walter Mondale by 9.4 points, meaning that there was swing of 26 points in just a few days.
Cases like these are why we say that the chance of Mr. Romney’s being upset are close to zero, but not exactly zero.
After three days spent on the ground here in New Hampshire, however — and after a deeper look at the polls — it certainly does not seem as though Mr. Romney is in any real danger.
By this point in 1984, Mr. Hart’s momentum in the polling would have been apparent. He had trailed Mr. Mondale by 30 points in the polls before his second-place finish in Iowa and was making up ground quickly.
No candidate seems to have that sort of momentum this year. Mr. Paul had a large and enthusiastic crowd at his rally in Nashua, but his polls have been flat or trending slightly downward. Rick Santorum initially gained ground after his showing in Iowa, but he was much further behind Mr. Romney, and one poll already shows Mr. Santorum’s momentum having stalled.
Meanwhile, New Hampshire is blanketed with Mr. Romney’s commercials, and with Mr. Romney yard signs at every highway median. And Mr. Romney is very well liked here: an NBC News/Marist poll found that only 16 percent of primary voters here would consider him an unacceptable nominee.