The New Hampshire primary is more “New” than Hampshire.

When discussing the nation’s first primary (it’s preceded by a newly controversial caucus), people often fall back on aphorisms about the area’s deeply rooted political culture and colonial heritage.

That certainly feels right. New Hampshire is one of the original 13 colonies. Its residents are among the nation’s oldest and whitest. It’s got a storied political tradition. It feels like a place where peoples’ roots go back for generations.

But the population is newer than you think. Only about 35 percent of the state’s voting-age residents were born there — easily the lowest rate in the Northeast, Census Bureau figures from 2018 show. Only a handful of migration magnets — such as Nevada, Florida and Arizona — rank higher.

Our analysis of responses from the Census Bureau’s annual American Community Survey shows today’s vote is as much of an expats from Massachusetts and New York primary as it is a New Hampshire primary.

The state’s unusual population composition has far-reaching electoral consequences, but we’ll leave that sort of in-depth analysis to our colleagues in politics, who have blanketed New Hampshire this winter. Here, we’re focused more on where people move more than on how they vote.

University of New Hampshire demographer Ken Johnson calculates that since the last election, about 195,000 of the state’s 1.1 million voters have departed — either from the state (150,000) or from this mortal existence (45,000). They’ve been replaced by about 230,000 fresh faces, including 70,000 young people who became newly eligible and 160,000 outsiders who moved in.

For one in five voters, this will be their first presidential primary in the state, according to Johnson’s latest calculations. Most of the state’s 2020 primary voters wouldn’t have been eligible to vote in 2008, when Hillary Clinton eked out a win over Barack Obama.

Johnson is himself a transplant. He moved from Chicago in 2007. Before he moved to New Hampshire, he said, he thought of the primary as an anachronism. But having seen several, and watched the population change, he’s come to appreciate how the nation’s first primary reflects an ever-changing American electorate.

New voters coming into the state are more liberal than those they replaced, Johnson said. “The differences are not huge,” he added, “but they could make a difference in a tight race like this.” These new voters belong to two very different waves: Millennial professionals and baby-boomer retirees.

“Migrants to New Hampshire include many families with children who settle in the state’s urban and suburban regions, as well as 50-69-year-olds who relocate to the state’s recreational and amenity areas,” Johnson wrote late last year.

To put New Hampshire’s numbers into context, we can look at mobility data from the American Community Survey. Every year, the Census Bureau asks more than 3 million Americans about subjects from their marital status to whether they have difficulty hearing. More importantly for this analysis, they also ask where you were born, where you lived last year and where you live now.

Typically, it takes about 60 years for a voter to move through the electorate, which is about how much longer a typical 18-year-old can expect to live, according to a 2017 estimate from the Centers for Disease Control and Prevention. But in states like New Hampshire, people move in and out so much that the majority of the electorate can change in a decade or two.

By contrast, almost three out of every four adults in Louisiana and Michigan were born in those states (74.8 and 73.0 percent, respectively). Ohio (71.3 percent) and Pennsylvania (69.9 percent) aren’t far behind. The electorates in those states, several of which were critical to Donald Trump’s success in 2016, won’t be quite as susceptible to swings caused by new arrivals.

If we look at the data by county instead of by state, we see that in places like New York, California and Texas, outsiders concentrate in massive metropolitan areas. But in places known primarily for their natural amenities, such as New Hampshire, Wyoming and Idaho, newcomers are a bigger presence in more of the state.

In New Hampshire, this combination of population turnover and population distribution has produced an unusual dynamic. In much of the United States, Democrats most often are clustered in urban areas, and Republicans tend to dominate rural areas.

But “in a nation increasingly polarized along urban-rural lines,” Johnson wrote last year, “New Hampshire provides the exception: a Republican Party increasingly concentrated in relatively densely populated counties, and a Democratic Party that displays geographic diversity.”

And that’s just one more reason to question your assumptions about today’s vote.