The state has seen a shift toward the GOP, which could enhance Romney’s conservative cred if he wins big.

Mitt Romney’s expected win in New Hampshire Tuesday could enhance his conservative bona fides. That’s because the Granite State has seen a remarkable growth in Republican influence in the last couple years and is poised to increase its pull on the national scene.

Traditionally, South Carolina primary voters were regarded as the gatekeepers of the GOP’s leadership. Win over the Palmetto State and you can lead the Republican Party, the conventional wisdom went, because South Carolina’s brand of conservatism was dominant. But New Hampshire, sometimes regarded as a blue state, is ripening to a deep red and could play an oversized role in not just the GOP nomination contest but the general election in 2012.

No state shifted more to the right in 2010 than New Hampshire. The GOP’s performance in New Hampshire last cycle is even more remarkable given that it came after the state had been trending solidly Democratic. Between 2004 and 2008, Democrats took over the governorship and both houses of the legislature, President Obama defeated Sen. John McCain (R-Ariz.) by 10 points and now-Sen. Jeanne Shaheen defeated Republican John Sununu in their 2008 Senate race rematch. After that cycle, you could have made a strong case that New Hampshire was becoming a blue state.

The 2010 elections, however, saw a dramatic reversal. Republicans were able to take back New Hampshire’s two House seats by healthy margins. And that was a mere prelude to the real surge made in other races. Both chambers of the state legislature flipped back to the GOP. But simply saying they flipped doesn’t do justice to the magnitude of the reversal. The state Senate went from 14 Democrats and 10 Republicans to 19 Republicans and 5 Democrats. The state House changed from 224 Democrats and 176 Republicans prior to the election to a whooping 298 Republicans and 102 Democrats after the 2010 vote. (The current make up is 293 Republicans, 104 Democrats and three vacancies).

Moreover, state Attorney General Kelly Ayotte won 61 percent of the vote in an open Senate race against Rep. Paul Hodes (D). According to Gallup, only Rhode Island saw a greater decline in Democratic Party identification from 2008 to 2010. Despite being in the heart of deep-blue New England, New Hampshire may be an easier win for the Republican nominee in 2012 than battlegrounds such as Ohio or Florida – particularly if Romney is at the top of the ticket.

Boston transplants make the state more Republican, not less. An observer to the previous decline of Republican fortunes in the state may identify the influx of Massachusetts natives as the prime cause for the shift. This is false. If anything, Massachusetts natives are the most Republican voters.

In 2004, 29 percent of voters originally were from Massachusetts. They gave George W. Bush 52 percent of the vote in his race against Sen. John Kerry (D-Mass.). That was about three points better than his overall performance in the state.

The most Republican towns in the state are those closest to the main corridors leading to Boston. The towns between the state line and Manchester on Interstate 93 are all solidly Republican. Derry, Windham and Salem are full of refugees from Massachusetts, and the inhabitants of these towns don’t want to further their former state’s political tradition — they want to escape it.

McCain won all but two of the towns in Rockingham and Hillsborough counties, which border Massachusetts. And Republicans won them all in convincing fashion in 2010. The mill cities of Manchester and Nashua are about at the state average for political partisanship, making them more Republican than typical northern working-class cities.

New Hampshire has always been a New England outlier. Before the Civil War, it was the Jacksonian outpost in Puritan New England.  Its only President, Franklin Pierce, was a pro-slavery Democrat, who was totally out of sympathy with the abolitionist Whig tradition that dominated New England society at the time. After the war, when the Republican Party was the political expression of New England, it was the most Democratic state in the region. It was the only state in New England to vote for Woodrow Wilson’s reelection in 1916.

It then transitioned to the best Republican state in New England while the region was shifting Democratic. It was Barry Goldwater’s most supportive state in the region and George McGovern’s least. It was the only state in New England that gave Reagan over 50 percent in 1980. Clinton won it merely by one point in 1992, far closer than in other New England states. And the only time Bush won a state in New England (or the Northeast) was when he won New Hampshire in 2000.

A version of this post was also published on Campaigns and Elections’  blog, Campaign Insider.