Senate Republicans who are up for reelection next year are sticking as close to President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE as possible, especially on his signature issue of illegal immigration and border security.

Even as some Senate Republicans broke with Trump over his emergency declaration to build a wall on the Mexican border, most of those running for reelection next year backed Trump — a sign of their fear of Trump-fueled primary opponents.

Only one of the 12 Republicans who voted on Thursday for a Democratic-backed resolution overturning Trump’s emergency declaration is up for reelection next year: Sen. Susan Collins Susan Margaret CollinsSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R), who has a well-established reputation in Maine as an independent.

ADVERTISEMENT

Republicans running in other swing states who arguably might have benefited from distancing themselves from Trump, such as Sens. Cory Gardner Cory Scott GardnerOvernight Health Care: US coronavirus deaths hit 200,000 | Ginsburg's death puts future of ObamaCare at risk | Federal panel delays vote on initial COVID-19 vaccine distribution The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (Colo.), Martha McSally Martha Elizabeth McSallyTumultuous court battle upends fight for Senate Grassley, Ernst pledge to 'evaluate' Trump's Supreme Court nominee The Hill's Campaign Report: Biden goes on offense MORE (Ariz.) and Thom Tillis Thomas (Thom) Roland TillisThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting OVERNIGHT ENERGY: EPA head questions connection of climate change to natural disasters | Pebble Mine executives eye future expansion in recorded conversations | EPA questions science linking widely used pesticide to brain damage in children Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight MORE (N.C.), stuck with him.

The tone was set early by Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellPelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Senate GOP aims to confirm Trump court pick by Oct. 29: report Trump argues full Supreme Court needed to settle potential election disputes MORE (R-Ky.).

The GOP leader, who is up for reelection, endorsed Trump’s national emergency declaration last month despite initially warning Trump against the move, according a Feb. 1 Washington Post report.

GOP strategists said Republicans have little choice given the potency of the issue of border security with Trump’s base.

“I think what they’ve seen is the Republican base has been energized by the issue the last couple years and it’s not going away,” said Chip Saltsman, a Republican strategist.

“This issue has really become a defining issue as you go into the next election cycle,” he added. “Donald Trump uses his bully pulpit very well, and he’s brought a lot of energy and focus on this issue, and they know he’s not going to stop talking about it.”

The Senate also delivered a rebuke to Trump on Wednesday when seven Republicans voted to pass a resolution requiring the president to withdraw U.S. military support from a Saudi-led coalition fighting in Yemen.

Only two of the defectors in that vote are up for reelection next year: Collins and Sen. Steve Daines Steven (Steve) David DainesTrump seeks to turn around campaign with Supreme Court fight McConnell locks down key GOP votes in Supreme Court fight Will Republicans' rank hypocrisy hinder their rush to replace Ginsburg? MORE (R-Mont.).

The issue of U.S. support for Saudi Arabia, however, has less salience with the GOP base than Trump’s promises to build a border wall.

A recent Politico/Morning Consult poll found that 70 percent of Republicans said they would be more likely to vote for a senator or representative who supports Trump’s national emergency declaration.

“The reason why you had Gardner and Tillis do this is because they knew that the process/principle argument wasn’t going to fly with the Republican base when this is their No. 1 issue. They want execution, and they don’t care how you get it,” said Ford O’Connell, a Republican strategist.

O’Connell said Gardner and Tillis, who have two of the most competitive races next year, need to worry about fending off primary challenges and turning out conservative voters in the election, when Democratic turnout is expected to be high.

“Even though they want to fend off primary challenges, this is also a situation where, in the general election, if they cross Trump on this issue, Trump could win their state and they could still lose,” he added. “In a lot of these races, it’s going to be two-point races, whether it’s Gardner or it’s Tillis.

Sen. Ben Sasse Benjamin (Ben) Eric SasseGovernment watchdog recommends creation of White House cyber director position Chamber of Commerce endorses McSally for reelection Ben Sasse is mistaken with idea for the election of senators in America MORE (R-Neb.) is in a slightly different position.

He’s not expected to face a difficult general election, but his repeated criticism of Trump’s conduct and policies has sparked talk of a possible primary challenge — if Sasse decides to run for another term. He said he will announce his decision this summer.

“Obviously Sasse is more concerned about a primary challenge,” O’Connell said, noting that Trump won Nebraska by 20 points in 2016. Sasse describes himself as a “constitutional conservative” and warned in a statement to National Review magazine in February that Trump’s emergency border declaration undermined the Constitution’s separation of powers.

He was seen as a likely vote in favor of the disapproval resolution, especially after several Senate GOP colleagues announced they would support it to preserve the Constitution’s separation of powers.

Sasse announced Thursday that he voted no because he saw it is a “politically motivated resolution” crafted by Democrats to embarrass Trump. He also noted his support for legislation to require Congress to approve future national emergency declarations after 30 days.

Trump emerged as a dominant force in Republican primaries in the 2018 midterm elections. Forty-nine of the 51 Republicans he endorsed in the 2018 primaries won their races, according to ABC News.

Tillis reversed himself on supporting the disapproval resolution after coming under pressure from conservatives in North Carolina.

He boldly voiced support for the resolution in a Feb. 25 Washington Post op-ed in which he warned that Trump’s use of the emergency declaration to secure more funding for border barriers would set a dangerous precedent that future Democratic presidents could exploit.

“Republicans need to realize that this will lead inevitably to regret when a Democrat once again controls the White House,” he wrote.

But Tillis came under withering criticism from conservatives at home, such as Diane Parnell, the chairwoman of the Rockingham County Republican Party, who urged conservative Rep. Mark Walker Bradley (Mark) Mark WalkerMike Johnson to run for vice chairman of House GOP conference The Hill's Morning Report - Sponsored by National Industries for the Blind - Woodward book revelations rock Washington The Hill's 12:30 Report — Presented by Facebook — Trump, Biden duel in final stretch | Vaccine trial on pause after recipient's 'potentially unexplained illness' | Biden visits Michigan | Trump campaign has 18 events in 11 states planned in the next week MORE (R-N.C.) to challenge Tillis in next year’s Senate primary.

“Trump has an approval rate of well over 80 percent among Republicans. That makes GOP Senators fear the President and worry that crossing him will lead to a primary challenger,” said Darrell West, vice president and director of governance studies at the Brookings Institution.

“It is hard to vote against the President on anything he has labeled a high priority. Doing that could lead to a Trump tweet that enrages the conservative base and creates problems for Republican lawmakers,” he added.

The one exception to the trend is Collins, but GOP strategists say she’s in a different category.

“Susan Collins has her own brand,” said Jim McLaughlin, a Republican strategist and pollster. McLaughlin said polling he’s seen of Republican voters in Maine shows she has strong support despite being a well-known moderate.

McLaughlin said Trump’s influence is more potent in Republican primaries where the person he endorses is running against someone without a well-defined brand.

Trump’s scored a coup in last year’s Florida gubernatorial primary when his endorsement helped then-Rep. Ron DeSantis Ron DeSantisTrump may meet with potential Supreme Court pick in Miami Florida governor unveils legislation targeting protesters in 'violent or disorderly' demonstrations Names to watch as Trump picks Ginsburg replacement on Supreme Court MORE (R-Fla.) overcome a 15-point deficit to defeat Adam Putnam and win the GOP nomination.

“Ron DeSantis — nobody knew who the heck the guy was. He got a couple tweets from the president and an endorsement, and the guy went from being down [big] to winning by a margin of nearly 2-to-1,” he said, citing DeSantis’s 56.5-point-to-36.5-point victory.