Senate Republicans are deeply concerned that Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE will cost them their majority, despite private assurances from leaders that voters opposed to the presumptive GOP presidential nominee will split their ballots.

A Washington Post-ABC News poll published last week shows Trump’s unfavorable rating has hit new a high, with 7 out of 10 respondents nationwide viewing him negatively.

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One Republican senator facing a competitive re-election said he and his colleagues are “very concerned.”

“There’s deep, deep concern,” he added.

Republicans have to defend 24 seats while Democrats only have to protect 10. Six of the vulnerable GOP seats are in states that President Obama won in 2008 and 2012.

Almost every day, Republican senators see new evidence of Trump’s lack of mainstream appeal.

Major companies such as Wells Fargo and UPS, which sponsored the 2012 Republican convention in Tampa, are skipping this summer’s event in Cleveland.

“There’s a lot of anxiety out there,” said a second Senate Republican. “People are trying to figure out what’s going on in the political climate, what it means to us, to me. There’s anxiety.”

Yet there’s a growing sense of resignation that not much can be done to change their presumptive nominee.

At a meeting of Senate Republicans at the National Republican Senatorial Committee headquarters Wednesday, Trump didn’t even come up for discussion, according to two lawmakers who participated.

Republican leaders are trying to buck up their nervous colleagues by arguing they can win re-election even if Trump crashes and burns.

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE (R-Ky.) predicted on Fox News that this will be a “ticket-splitting kind of year.”

He believes that many people who vote for Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE, the likely Democratic nominee, or Gary Johnson Gary Earl JohnsonWhat the numbers say about Trump's chances at reelection Presidential race tightens in Minnesota as Trump plows resources into state The Hill's Campaign Report: Biden condemns violence, blames Trump for fomenting it l Bitter Mass. primaries reach the end l Super PAC spending set to explode MORE, the libertarian nominee, will also vote for Republican Senate candidates.

He is urging vulnerable incumbents to distance themselves from Trump and run their own races.

Republican Sen. Mark Kirk Mark Steven KirkLiberal veterans group urges Biden to name Duckworth VP On the Trail: Senate GOP hopefuls tie themselves to Trump Biden campaign releases video to explain 'what really happened in Ukraine' MORE (Ill.), the most endangered Senate incumbent, has taken that advice and withdrawn his endorsement.

“He is too bigoted and racist for the land of Lincoln,” he told The Hill, adding that other Senate Republicans “could” be concerned about his effect on their own contests.

NRSC Chairman Roger Wicker Roger Frederick WickerHillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll Shakespeare Theatre Company goes virtual for 'Will on the Hill...or Won't They?' Republican Senators raise concerns over Oracle-TikTok deal MORE (Miss.) said Trump won’t necessarily have a negative impact on Senate candidates.

“That hasn’t happened historically,” he said of fears that the nominee will create headwinds in Senate races. “Our candidates look very, very good. We’ll take [the races] one by one.”

Other Republicans make the same argument.

“I believe that people vote individually, evaluating each race. We have very strong Senate candidates and they will run their own races,” said Sen. Susan Collins Susan Margaret CollinsJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally Momentum growing among Republicans for Supreme Court vote before Election Day MORE (R-Maine), who is not up for reelection this year.

In recent elections, however, the macro political environment has had as big an impact on results and candidate quality, experts say.

“They’re whistling past the graveyard,” said Larry Sabato, director of the University of Virginia’s Center for Politics, when asked about GOP skepticism of a presidential coattail effect in 2016. “To deny there’s coattails is laughable. It’s a very polarized era.”

In a report published last year, UVA’s Center for Politics observed the correlation between presidential and Senate voting exceeded 80 percent in the past two presidential elections.

Democrats picked up two Senate seats when Obama was re-elected in 2012, winning races in five Republican-leaning states: Indiana, Missouri, Montana, North Dakota and West Virginia. They also won in the swing states of Florida, Ohio and Virginia.

Democrats won a net gain of eight Senate seats in 2008, when Obama first captured the White House.

Karl Rove, who served as former President George W. Bush’s top political advisor, predicted in December that the top of the ticket will have a major influence on November’s Senate races.

“In the past two presidential contests, the Republican ticket’s downward pull on the party’s Senate candidates was pronounced,” he wrote in a Wall Street Journal op-ed, noting that Senate Republican incumbents lost in New Hampshire and Oregon in 2008 despite running ahead of their presidential nominee, John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE.

Senate Republicans picked up four seats when Bush won re-election in 2004.

In 2014, losing Senate Democratic incumbents such as former Sen. Mark Begich Mark Peter BegichAlaska group backing independent candidate appears linked to Democrats Sullivan wins Alaska Senate GOP primary Alaska political mess has legislators divided over meeting place MORE (Alaska) blamed their losses on President Obama’s unpopularity.

Begich, who was thought to have run a near-perfect race, observed to the Alaska Dispatch that the Republican strategy that year was to make every race about Obama.

Republicans say this year will be different because unlike in past presidential elections, their candidates won’t embrace the nominee.

Sen. Kelly Ayotte Kelly Ann AyotteBottom line Bottom line Bottom Line MORE (R), who has a tough race in New Hampshire, for example, has emphasized that she will support but not endorse Trump.

Democratic strategists say it will be impossible for Republican candidates to inoculate themselves from Trump’s unpopularity. The Democratic Senatorial Campaign Committee has launched a campaign branding the GOP as “the party of Trump.”

Adam Jentleson, a senior aide to Senate Democratic Leader Harry Reid Harry Mason ReidGraham signals support for confirming a Supreme Court nominee this year Trump signals he will move to replace Ginsburg 'without delay' Senate Republicans signal openness to working with Biden MORE (Nev.), on Thursday called Sen. John McCain (R-Ariz.) and his fellow Republicans “puppets of Trump” after McCain blamed Obama’s national security policies for the mass shooting in Orlando. McCain is facing the toughest race of his Senate career,

Trump’s penchant for shooting from the hip and sparking media frenzies has overshadowed Republican accomplishments in Congress.

Senate Republicans were hoping to spend the week of June 6 discussing the disappointing May jobs report, which showed employers added only 38,000 workers to their payrolls.

Instead, Trump’s comments attacking a Mexican-American judge presiding over a lawsuit against Trump University dominated the political debate, putting vulnerable Senate incumbents on the defensive.

“If he had just said nothing and let the jobs report speak for him, it would have been a great week,” said another GOP senator facing a tough re-election.

Trump’s most stomach-churning characteristic, according to many Senate Republicans, is his sheer unpredictability.

He surprised allies by tweeting Wednesday that he would be meeting with the National Rifle Association about not allowing people on terror watch lists from buying guns, a position that most Senate Republicans oppose without sufficient due-process safeguards.

Trump’s unexpected statement immediately put Republicans who voted in December against legislation sponsored by Sen. Dianne Feinstein Dianne Emiel FeinsteinMcConnell says Trump nominee to replace Ginsburg will get Senate vote Top Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence Intensifying natural disasters do little to move needle on climate efforts MORE (D-Calif.) banning people on the no-fly list from buying guns on the defensive.

The entire Senate GOP conference except for Kirk voted against it.