Centrist Republicans are alarmed over the potential impact of nominating Donald Trump or Ted Cruz on efforts to retain seats
Brian Dooley, a New Hampshire Republican, represents the GOP’s biggest fear: a voter who would rather stay home on Election Day than support the party’s current front-runners.
“It would give me pause. It’s like pick your poison,” said Mr. Dooley, a 57-year-old Nashua Republican activist, of the prospect of voting for businessman Donald Trump over leading Democratic contender Hillary Clinton.
The top of the ticket could have implications for turnout that affect the outcome of races further down the ballot, particularly on the GOP side.
Senate Republicans will defend 24 seats in November, with 10 of them in competitive states, according to political tracking services. State polls show New Hampshire’s Senate race is one of the tightest, with incumbent Sen. Kelly Ayotte facing Democratic Gov. Maggie Hassan.
“With Trump, you either like him or hate him,” said former state Republican Gov. John Sununu, a former chief of staff for President George H.W. Bush who is staying neutral during the primary. “If Trump is the nominee, Republicans could lose the Senate and could even lose the House.”
The Trump and Cruz campaigns dispute that assessment, saying their candidates will bring out disenfranchised voters who would fill the gap if others stay at home.
Mr. Trump’s influence on down-ballot races “would be the exact opposite,” said Hope Hicks, his spokeswoman. The real-estate developer has inspired fervor among a swath of blue-collar voters and Reagan Democrats, and their votes would buoy the Republican ticket, his supporters said.
Mr. Cruz has said his nomination will drive evangelical Christians who sat out the 2012 general election to the polls. Catherine Frazier, his campaign spokeswoman, said Republicans with conservative platforms helped the GOP gain congressional seats last year.
“Every election cycle, this is the same flawed narrative pushed by establishment Republicans,” she said.
That the downstream consequences of a Trump or Cruz candidacy are being debated in the party shows how seriously many are taking the possibility and highlights a split between the GOP’s establishment and its grass roots. The first votes will be cast in just a few weeks
The party in Washington is trying to keep its majority in the Senate, where it holds 54 of 100 seats. Its majority in the House is relatively safe.
Among GOP Senate incumbents who could face tough challenges are Rob Portman in Ohio, Pat Toomey in Pennsylvania, Ron Johnson in Wisconsin, John McCain in Arizona, Mark Kirk in Illinois and Ms. Ayotte in New Hampshire.
“Obviously if we have a presidential candidate who is doing well in purple states, it would make it easier for us to have a majority in the next Congress,” said Senate Majority Leader Mitch McConnell of Kentucky. Mr. McConnell declined to say which nominees would best help GOP prospects in battleground states.
All the Senate candidates have said they would support the eventual GOP presidential nominee. Democrats will also do everything they can to tie Mr. Trump’s controversial proposals to the incumbents.
“It eliminates paths to victory for these candidates,” said Lauren Passalacqua, press secretary for the Democratic Senatorial Campaign Committee.
A Real Clear Politics average of national polls of GOP primary voters showed Mr. Trump with 34% support and Mr. Cruz with 18%. Sen. Marco Rubio (R., Fla), competing in the conservative and centrist lanes, ranked third with 12%.
In a hypothetical general-election contest with Democratic front-runner Hillary Clinton, Mr. Trump received 40% of support compared with 50% for the Democrat, according to an NBC News/Wall Street Journal poll this month. The split was closer with Mr. Cruz, who received 45% support to Mrs. Clinton’s 48%.
Democrats, who have 10 seats up for grabs, aren’t immune to some of the same tensions, especially if Vermont Sen. Bernie Sanders unexpectedly wins the nomination. Mrs. Clinton, too, while riding high in polls, won’t automatically lure President Barack Obama’s diverse coalition and is a divisive figure among Republicans. That could inhibit the party’s bid to take the GOP Senate seats.
New Hampshire politics have been upended by hard-line positions taken by Messrs. Trump and Cruz on immigration and Muslims. After state GOP chairwoman Jennifer Horn called Mr. Trump’s proposed ban on Muslims entering the U.S. “divisive,” his state supporters mounted a petition drive for her to resign.
“These are the type of people who need to learn that we aren’t in the business of picking winners and losers,” said Joshua Whitehouse, a New Hampshire state representative and Trump supporter.
A spokesman for Ms. Horn declined to make her available for comment.
Ms. Ayotte said she is focusing on her own race. “The people of New Hampshire will play a major role in selecting the Republican nominee, and I have confidence in New Hampshire’s role in that process,” she said.
Many Republicans and independents in the state said they would vote for the GOP nominee come November no matter what. Others weren’t so sure. “Our kids hate Donald Trump,” said Patte Powers, a Bedford retiree with three children who vote independent. “That will cause them to go out and vote for someone else just to cancel out the [Trump] vote.”
Pennsylvania Republicans are worried about an antiestablishment nominee’s impact on Sen. Toomey’s re-election. The state GOP kept Mr. Trump as a fundraising speaker earlier this month despite the protest of some party leaders.
Ted Kwong, a spokesman for Mr. Toomey’s campaign, said voters choose candidates individually. “We’re confident they support Pat Toomey’s thoughtful and constructive approach,” he said.
Ohio GOP chairman Matt Borges said they were prepared to defend GOP incumbents in the face of a nominee pitching “a bad product.”
“We just have to run our campaign a little differently,” he said. “Is it ideal to do that? No.”