Sen. Jon Tester has a problem. Politicians want elections to be as predictable as possible.

Yet there is a HUGE wild card in the election for Senate in 2024 and it is unclear whether or not it helps him. The fresh population of wealthier residents — often retirees, technology workers able to do their jobs remotely and other big-city transplants — is one of the largest question marks hanging over Montana’s crucial race for Senate. As Jon Tester, the Democratic incumbent, looks to fend off Tim Sheehy, a businessman and retired Navy SEAL who is expected to capture the Republican nomination, tensions over the exploding growth will be a top issue in November.

And how the new Montanans vote could prove decisive. On the surface, their presence might seem to benefit the embattled Mr. Tester, because a sizable chunk of them — 35 percent of arrivals in 2022 — hail from left-leaning states like California, Colorado, Oregon and Washington, according to census data analyzed by the real estate firm CBRE.

Some political experts, though, believe the arrivals could tilt more to the right, noting a broader phenomenon in which conservatives have left their home states in part because of what they see as liberal overreach. “Especially during the pandemic, there was movement from people out of more blue areas looking for a different, kind of more Republican, way of life,” said Dr. Jessi Bennion, a professor of political science at Montana State University.

“My best guess is that a.