Sen. Kelly Ayotte (R-N.H.), who is up for reelection this year, has said she supports but does not endorse Donald Trump’s presidential bid. (Alex Brandon/AP)

Sen. Patrick J. Toomey (R-Pa.) said he hadn’t thought about it. Sen. Kelly Ayotte (R-N.H.) sidestepped it. Sen. John McCain (R-Ariz.) insisted that he had said enough.

The question they faced: Would you campaign with Donald Trump?

“I’m campaigning for myself,” Ayotte said on a walk in the underground tunnel from the U.S. Capitol building to the Senate offices. An aide interjected to say that they were late for a meeting, cutting short the conversation.

“I have one priority and that’s campaigning for myself,” Ayotte added as she walked away.

One after another, Republican senators on the front lines of the effort to hold their fragile majority dodged, diverted or acquiesced halfheartedly when asked if they would appear with Trump on the campaign trail. As the Manhattan mogul cements his position as the GOP standard-bearer, these down-ballot contenders are trying to save their jobs by running away from their party’s presumptive nominee.

Sen. Pat Toomey, R-Pa., arrives for a news conference, Monday, May 9, 2016, in Philadelphia. (Matt Rourke/AP)

The dynamic underscores the tightrope that at-risk Republicans are attempting to walk with Trump, who commands a devoted following within the GOP base but is entering the general-election race with historically low favorability ratings, especially among women and minorities. And although the party is for the most part coalescing around Trump, the hesitance to campaign with him shows that there are limits to how fully Republicans are willing to embrace him — at least for now.

“I’m going to run, you know, my own campaign and if he wants to help me that’s fine,” said Sen. Rob Portman of Ohio, a state expected to be a key presidential battleground again.

What if Trump offered to campaign with Portman?

“I’m going to have my own campaign out there and do my own thing,” Portman repeated. “So I don’t know that that’ll happen. But if he wants to help, that’s fine.”

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During the 2014 midterms, vulnerable red- and purple-state Democratic senators tried unsuccessfully to outrun President Obama’s unpopularity as Republicans relentlessly tied them together. Given the close historical link between the outcome of presidential and congressional elections, Democrats are wagering that they can turn the tables in November by tethering blue- and purple-state Republicans to Trump in areas that they hope Hillary Clinton will carry.

The Democratic Senatorial Campaign Committee has been promoting a website that encourages visitors to “Meet the ReTRUMPlicans.” It features a video showing Republican senators pledging to support the GOP nominee and some of Trump’s more controversial moments, including his mocking of a reporter with a disability. Other Democratic groups are planning similar efforts.

Sen. Rob Portman (R-Ohio) sounds less than enthusiastic about campaigning with Donald Trump: “ I’m going to run, you know, my own campaign and if he wants to help me that’s fine.” (John Minchillo/AP)

Anticipating the Democratic onslaught, Republican senators have committed to running heavily localized campaigns. The National Republican Senatorial Committee’s mantra: Run as if you are running for sheriff.

Ayotte and Portman are two of the GOP’s top priorities on a map that was ripe for Democratic gains long before Trump emerged as the nominee. Republican officials have identified GOP Senate seats in New Hampshire, Ohio and Pennsylvania, as well as a Democratic seat in Nevada, as decisive battlegrounds.

Democrats can win the Senate majority by gaining four seats. They view three — Illinois, Wisconsin and Florida — as particularly promising. Senate Republicans are defending seven seats in states that Obama won twice.

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Both parties are aggressively targeting Pennsylvania, where the Democratic presidential nominee has won every election since 1992. Asked whether he would campaign with Trump, Toomey said: “I haven’t thought about that. I’m running my own campaign.”

But in a local radio interview quickly publicized by Pennsylvania Democrats last week, Toomey wouldn’t rule out campaigning with the mogul.

Kevin McLaughlin, the deputy executive director of the NRSC, the Senate Republicans’ campaign arm, said that the committee is not instructing its candidates to take a uniform position when it comes to campaigning with Trump. “There is no blanket answer for everything,” he said.

There are signs that running the kind of personalized campaigns that Republican leaders envision will be difficult. Ayotte and Sen. Ron Johnson (R-Wis.) recently attracted widespread attention for trying to distinguish between supporting and endorsing Trump. Democrats believe that Republican senators will find themselves so contorted over Trump that it will overshadow their messaging.

Trump’s campaign appears content to help from afar by taking part in a joint fundraising effort with the Republican National Committee to raise money for Senate and House races. The presumptive nominee huddled with top Senate Republicans at NRSC headquarters during a rapid-fire round of meetings in Washington this month. GOP leaders said both sides understood that some Senate Republicans would distance themselves from Trump.

“Yeah, they care about it, although I don’t sense that they’re in any way intimidated or panicked by it because they’ve been running against the establishment all along,” said Sen. Jeff Sessions (R-Ala.), a Trump backer who has recently spoken directly to him.

Trump campaign manager Corey Lewandowski said that in addition to fundraising help down the ballot, the campaign’s main assistance will come in boosting turnout for Republicans.

“Right now we’re interested in our race and to make sure we have the strongest candidate on the top of the ballot,” he said.

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Asked about the reluctance of many vulnerable Republican senators to commit to campaigning with Trump, Lewandowski pointed to Trump’s dominating primary finishes in places such as Pennsylvania and New Hampshire and to polling that shows a close contest with Clinton.

While Democrats are eager to use Trump to their advantage in competitive Senate contests, Republicans see an opportunity to use Clinton’s image problems — polls show many Americans distrust her and that many Republicans strongly dislike her — as an opportunity in races further down the ballot.

Pressed whether Sen. Richard Burr (R-N.C.) would appear with Trump, his campaign responded with a statement saying that Burr “looks forward to working with Mr. Trump at the top of the ticket” and added: “There will not be a third term for a Clinton/Obama Administration in the White House.”

One of the toughest states for Senate Republicans will be Wisconsin, where Trump lost in the primary. The Badger State has voted for the Democratic presidential nominee seven times in a row.

“Right now it’s hypothetical,” Johnson said when asked about the prospect of appearing with Trump. “I have no idea what his campaign strategy is going to be.”

Even in states that look more challenging for Democrats, the Republican incumbents are treading carefully. If the election turns into a strong anti-Trump wave, Democrats think, underdog challengers could ride it to victory in states that seemed to be safely Republican only a few months ago.

“I’m campaigning [on] my own in Arizona,” McCain said. Pressed on whether he would campaign with Trump, McCain said: “I’ve said enough about Mr. Trump.”

Sen. Chuck Grassley (R-Iowa), who hasn’t faced a close race since he was first elected to the Senate in 1980, said: “I’m in a position where I’m going to run my campaign as if this is the toughest campaign I ever had.”

What about campaigning with Trump?

“He’d have to call me a month ahead of time,” Grassley responded, “because I’m going to be scheduled a month ahead of time.”

Mike DeBonis and Paul Kane contributed to this report.