Fryeburg, Maine Tip O’Neill liked to say that all politics is local. In our era of partisan and ideological polarization, politics has become far more national. But a pair of Senate campaigns in northern New England may defy this trend. At a time when Democrats are running competitive races in red states, Republican candidates in Maine and New Hampshire are keeping their races close despite the Donald Trump undertow and their states’ Democratic inclinations.

Sen. Susan Collins of Maine and former Sen. John E. Sununu of New Hampshire are running on their strong personal brands with an emphasis on constituent services and localism. Localism remains strong in Maine partially because the state is unusual. It has the oldest median age and the second-highest proportion of residents living in rural areas (behind Vermont) among all 50 states. The economy is built on agriculture, natural resources, shipbuilding, manufacturing and lobstering.

Mainers tend to be socially liberal and are 10 percentage points likelier to be religiously unaffiliated than the national average. That makes it unsurprising that Ms. Collins, a centrist pro-choice Republican who grew up in the rural northeastern part of the state, has won five terms.

As Senate Appropriations Committee chairman, Ms. Collins has secured significant funding for state projects. During her visit on Oct. 9 to the state’s largest agricultural fair, in Fryeburg, fairgoers thanked her for projects and services including the construction of fire stations. “That kind of constituent service,” Ms. Collins said in an interview, “really matters to people’s quality of life.”

In more than two hours at the fairgrounds, the senator rarely walked more than a few feet before being approached by a Mainer expressing appreciation or asking her to pose for a photo. “Most Mainers understand that I always put Maine first,” she said. “And that’s my reason for serving.”Her Democratic challenger, Troy Jackson, portrays Ms. Collins as a partisan—“Donald Trump owns her,” he said last month—but her voting record tells a different story.

She is consistently ranked as one of the most bipartisan senators and has often broken with Mr. Trump. She opposed repealing the Affordable Care Act in 2017, arguing that repeal without replacement would harm Maine’s low-income seniors and rural hospitals. She voted against the One Big Beautiful Act for the same reason. She has voted five times against tariffs and nine times against the war with Iran.

Ms. Collins says she aspires to be “a workhorse, not a show horse” and to remain above the partisan fray, brokering agreements across the aisle. But the Democratic Party is making the race about partisan national politics. That didn’t work in 2020, when the party and political committees allied with it spent millions to unseat Ms. Collins. She won by 8.6 points while Joe Biden carried the state by 9.

Mr. Jackson makes an issue of Ms. Collins’s vote to confirm Justice Brett Kavanaugh in 2018—never mind that she opposed Justice Amy Coney Barrett two years later on grounds that it was too close to a presidential election, and she voted to confirm Justices Sonia Sotomayor, Elena Kagan and Ketanji Brown Jackson. Nonetheless, this appeal resonates with some Mainers. “I have voted for her before, but I feel very disappointed in how she voted for Kavanaugh,” said fairgoer Karen Speel, 54, of Old Orchard Beach, who plans to vote for Mr. Jackson.

Left-leaning media have piled on. ProPublica last month featured a convicted felon’s accusations of corruption against Ms. Collins. She denies wrongdoing, and the Federal Bureau of Investigation questioned the veracity of the felon’s account and closed its inquiry.

Mr. Jackson, who declined to be interviewed, is running on a populist platform in line with leftist Democrats’ national priorities: for “Medicare for all,” strong unions, more-generous Social Security benefits, higher taxes on the rich; against “genocide in Gaza.”He hopes Mainers will reject their longtime senator to push back on Mr. Trump’s agenda.

That’s the pitch Sen. Bernie Sanders has been making while stumping for Mr. Jackson. “I know that there are many people in Maine who like Susan Collins,” the self-styled socialist from Vermont said at an Oct. 11 rally in Lewiston. “But if you want—if we as a nation want—to hold Trump and his disastrous policies accountable, the only way we can do that is by electing a Democratic Senate.”

Mr. Jackson’s campaign has strong support in the heavily Democratic southern part of the state. I saw myriad yard signs in Portland. At the Lewiston rally, some attendees said they are supporting Mr. Jackson mostly for national political reasons. “I like Jackson more than Graham Platner, but I’m not a huge fan. It’s more a vote against Trump,” said Carrie Girardin, 38, of Buckfield. (Mr. Platner, who won the Democratic primary, withdrew from the race amid allegations of sexual assault, which he denied.)

Yet many Mainers said that while they are anti-Trump, they plan to vote for Ms. Collins because she delivers for Maine. John Moss, 37, of Windham, says he sees the candidates as “two poor choices” but plans to pull the lever for Ms. Collins. Mary Watson, 78, of Standish, says: “I could still change my mind.”

Recent polls show Mr. Jackson with a narrow lead, but Ms. Collins has a strong base of support and a history of surviving Democratic wave years. She trailed her challenger in 2020 polls too.

In New Hampshire, Republican John E. Sununu seeks the open seat being vacated by Jeanne Shaheen, who defeated him when he sought a second term in 2008. His opponent is Rep. Chris Pappas. As I drove across the state line, I saw similar landscapes—rolling hills and vivid fall leaves. But there are many differences between the two states.

New Hampshire is one of the most college-educated states. It is significantly more suburban than Maine, and median household income is more than $24,000 higher. Important industries are advanced manufacturing, life sciences, technology, tourism and healthcare. Granite Staters are considerably more secular than Mainers—19 points likelier to be religiously unaffiliated than the nation as a whole. They also tend to be socially liberal, but they lean toward fiscal conservatism.

New Hampshire has no state income or sales tax, making it a magnet for overtaxed residents of Massachusetts. The state’s motto, “Live Free or Die,” captures its libertarian ethos.

No Republican presidential candidate has carried New Hampshire since 2000, and the state’s House delegation has been all Democratic since 2017. But the state Legislature is GOP-controlled, Republican Kelly Ayotte is governor, and the GOP has a 4-1 majority on the state’s elected Executive Council, which controls the budget. State Executive Dave Wheeler said in an interview that Granite Staters elect fiscal conservatives to state office because “they’ve seen what they get, what Republicans have delivered.”

Mr. Sununu is a New Hampshire scion. His father, John H. Sununu, served as governor (1983-89) before becoming George H.W. Bush’s White House Chief of Staff. The former senator’s brother, Chris Sununu, also served as governor (2017-25). John E. Sununu represented New Hampshire in the House (1997-2003) before his Senate term (2003-09), then lost re-election in a Democratic wave year. Mr. Sununu’s political philosophy is the New Hampshire way.

When running for re-election in 2008, he told journalist P.J. O’Rourke that Americans are best served by “limited and effective government,” low taxes and “local governance to the greatest extent possible.”“This is a guy who has shown a true willingness to basically cut his own direction and be independent and focus on what he thinks is best for New Hampshire,” said Greg Moore, state director for Americans for Prosperity, which has knocked on nearly 300,000 doors for the Sununu campaign.

While in Washington, Mr. Sununu broke with his party to oppose a constitutional amendment against same-sex marriage, sponsored legislation that protected more than 30,000 acres of the White Mountain National Forest, voted to increase home heating assistance for low-income households and fought the Pentagon’s recommendation to close the Portsmouth Naval Shipyard, an economic engine for the state. More recently, he has spoken out against tariffs on Canada and the Iran war. He is also talking about making Social Security solvent; his would be a rare voice of fiscal discipline in Washington.

Mr. Pappas is a run-of-the-mill Democrat. The Sununu campaign provides records showing that Mr. Pappas voted with former Speaker Nancy Pelosi in 222 out of 223 recorded votes, and for higher taxes 68 times. He also voted against final passage of a package authorizing more than $189 million for the Portsmouth Naval Shipyard. And although he casts himself as mainstream, he has declined to condemn socialism. Mr. Pappas didn’t respond to interview requests.

Mr. Sununu declined to be interviewed; his spokesman said the campaign “has made a concerted effort to keep the race focused on New Hampshire and state issues and has subsequently declined most national requests.”Mr. Pappas leads every poll, but by single digits. Over a plate of chicken tenders at the Puritan Backroom Restaurant in Manchester, owned by generations of the Pappas family, I talked with New Hampshirites. Denise Gosling, 73, of Bow, said she plans to stick with Ms. Ayotte for governor but is “definitely voting for Chris” for Senate.

When I later spent 2½ hours shadowing Americans for Prosperity’s door-knocking campaign in Manchester, other residents of the state’s largest city also said they support the governor or are undecided but will vote for Mr. Pappas to stop Mr. Trump.

This doesn’t surprise Mr. Wheeler of the Executive Council, who notes that owing to educational levels and the state’s traditional first-in-the-nation primary status, Granite Staters are politically sophisticated and often view state and federal races through separate lenses. Even so, he is optimistic about Mr. Sununu’s chances: “I think it’s a very close race.”Polls in New Hampshire close early, at 7 p.m. Eastern Time, and in Maine at 8. We’ll have to wait for other results to see if these states follow the national mood or buck it. Ms. McClain is assistant editorial features editor at the Journal.