Kamala Harris’s selection of Gov. Tim Walz of Minnesota as her running mate was, like most events of this turbulent political season, mostly unforeseeable just a few weeks ago.

Instead of bolstering her ticket with a Democrat from a crucial swing state — or even one who routinely elected Republicans up and down the ballot — seemingly at the 11th hour, Ms. Harris opted for Mr. Walz, a 60-year-old former congressman. Mr. Walz is a white Midwestern governor from a largely agrarian state. His selection holds the potential of winning back some of the rural regions and even states that are now staunchly Republican. This could make for a winning strategy in the Electoral College, which is now daunting for Democrats.

Mr. Walz will be a potent weapon Ms. Harris can readily deploy on her behalf. But he carries downsides that shouldn’t be overlooked, beginning with geography and extending to his time as governor during a period of immense upheaval for Minnesota and the country.

Mr. Walz’s strengths are clear: He spent over a decade as a public-school teacher and football coach and served in the Army National Guard; in 2006, he flipped a Republican-held House district in rural Minnesota and beat back G.O.P. opposition in several trying election cycles. He’s relatively progressive and a gun owner.

Democrats have several enormous challenges that the Harris campaign, no matter how well it might function, cannot readily solve. The selection of Mr. Walz could help remedy the problem of working-class voters who have been bleeding out of the Democratic coalition, especially since Donald Trump won the presidency in 2016. White voters are by far the largest segment, but there have been defections from socially conservative Black and Latinos, as well.

Two other factors work in his favor: Progressives like him, and he performs well on television. The latter may have mattered even more to Ms. Harris’s team. Mr. Walz rocketed to prominence by lashing Republicans as “weird,” which became something of a rallying cry after the criticism of JD Vance’s comment about “childless cat ladies.”