Of course, not all blue-state migrants are liberal. And people’s political views can change over time. But enough of the migrants have the views of their home states to have made a difference. It’s no accident that the places in once-red states where migrants have tended to settle — like the Virginia suburbs of Washington, the Research Triangle of North Carolina and the Denver metro area — are the places that have allowed Democrats to overcome huge deficits elsewhere in those states. Many of these migrants are Northeastern Democrats.

Colorado has gained twice as many migrants from blue states as from red since 2000, and blue-state expats now make up 12 percent of the population. In North Carolina, blue migration is occurring four times as quickly as migration from red states, and blue-state natives now account for 16 percent of the North Carolina population. (In each case, locally born residents still make up the majority.)

On the flip side, the movement of blue-staters into Texas, Utah and Idaho hasn’t helped Democrats as much, in part because many of the migrants are more conservative voters, such as whites from Southern California. Texas and the interior West have also drawn more red-state migrants than states where Democrats have recently won.

Even with the growing blue diaspora, the Democrats face an uphill battle in holding on to the Senate this year. The Upshot’s forecasting model, based on a combination of polls, fund-raising numbers, demographics and other data, gives the Republicans a slightly better than 60 percent chance of winning Senate control in November. And political analysts give Democrats almost no chance of winning the House of Representatives. But perhaps the smartest way to look at these trends is through a long-term prism. Blue-to-red migration has been happening for decades, and there are reasons to think it will continue.

If demographic changes don’t overturn the political reality this year, they still may in the future. Consider this: Since 1980, the population of New Yorkers living in New Jersey — a very common arrangement — has increased by the same amount as the New York-born population of South Carolina.