Republicans are increasingly worried that Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE’s candidacy will hurt the party’s quest to maintain the Senate majority in 2016.

The real estate mogul’s controversial comments on immigration could cause a trickle-down effect and haunt Republican Senate candidates, party strategists say.

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“I think it’s pretty clear that some of [Trump’s] more dramatic proposals on immigration will certainly affect races like the Nevada Senate race in particular," said one Nevada GOP strategist.

The debate over Trump's immigration stance “will, by its very nature spill down to races,” the strategist said.

“In a state like Nevada, the Hispanic element is absolutely essential.”

Florida GOP strategist Rick Wilson, who is advising Florida Senatorial candidate, Lt. Gov. Carlos Lopez-Cantera, thinks that "in the big picture, all of these candidates will stand or fall on their own strengths."

But, he added, “the worst case scenario is that Trump is running a campaign that is only about Trump, and [GOP Senate candidates] are constantly under the gun and trying to answer the latest policy announcement he makes.”

Wilson said the landscape has the potential to resemble 2006, where Republican candidates were dogged by President George W. Bush’s sinking popularity in the midterm elections. Democrats took back control of both the House and the Senate that year.

Indeed, GOP Senate candidates — including Sens. Kelly Ayotte (N.H.), Mark Kirk (Ill.), John McCain (Ariz.) and Sen. Richard Burr (N.C.), as well as Rep. Joe Heck (Nev.) — have all been asked about Trump’s stances on the trail.

Ayotte, Kirk and Heck have criticized Trump’s controversial comments on immigration, while Burr said Thursday that he is “delighted” by Trump’s passion.

Democrats have already capitalized on Trump’s presence in the race.

They slammed Burr on his comments in a release to reporters, asking if Burr found three controversial Trump statements “delightful.”

They are also aiming for other Republican candidates. With the Senate map already favoring Democrats, the party needs just four seats to take back the Senate if it retains control of the White House.

The GOP is defending 24 Senate seats, with as many as nine in play. Democrats are defending 10 seats, all but two in relatively safe states.

New Hampshire Democratic Party Chairman Raymond Buckley sought to tie Ayotte to Trump, calling her past support of ending birthright citizenship “another example of how perfect Donald Trump and Kelly Ayotte are for each other.”

Sadie Weiner, the Democratic Senatorial Campaign Committee’s spokeswoman, told The Hill that the group is happy to sit back and see how the Trump effect plays out, but could seek to similarly conflate Trump and GOP Senate candidates.

“He is doing most of the work for us in terms of going out there and saying these racist, offensive to all people comments and candidates are getting asked about it on the trail. People are drawing their own dots,” she said.

“I’m sure down the road, it would be something that we would look at, but at this point it is happening pretty organically without much pushing from us.”

By far, immigration is the issue most likely to create problems for Senate candidates, especially in states with a large Hispanic population.

Hispanic voters made up 16 percent of eligible voters in Nevada in 2014, 17 percent in Florida and 10 percent in Illinois according to the Pew Research Center. The group also makes up about 14 percent in Colorado, but Republicans haven’t coalesced around a major candidate for that seat.

While most of the other contentious states had a low single-digit share of eligible Hispanic voters in 2014, that constituency could still prove important in a race separated by a few percentage points.

Victoria M. DeFrancesco Soto, an outreach coordinator at the Center for Mexican American Studies at The University of Texas at Austin, said that backlash against Trump’s comments in which he referred to Mexican immigrants as "criminals, drug dealers, rapists" could mobilize the Hispanic electorate in many of those states.

“When you have such sharp, anti-immigrant rhetoric, you are going to have a boomerang effect,” she said.

But there’s disagreement among Republicans over whether Trump’s immigration rhetoric will stick to the party for the long haul.

Before Trump’s poll numbers shot up, a July Univision poll found that while 79 percent of Hispanics found his earlier comments on Mexican immigrants offensive, only 14 percent said that they felt the statements represent the GOP.

Many strategists fret that Trump’s controversial comments could hurt the party’s brand as a whole, but they are confident that individual candidates can weather that storm.

The Nevada GOP strategist said that Heck, the state’s leading GOP Senate candidate, has made an effort to build a broad coalition to include Hispanics.

That, he believes, will insulate Heck from significant damage from Trump’s comments. The strategist added that he would advise candidates looking to attract Hispanic voters to provide a stark contrast to Trump’s immigration stance.

Pat Brady, an Illinois Republican strategist and former state GOP party chair, admits that Trump’s message does “a lot of damage to Illinois Republicans” as far as the party’s work to put the state back in play for the presidential race.

But he countered the assertion that Trump’s rhetoric would sway voters against Kirk, who is fighting to keep his Senate seat.

“They are never going to equate anything Donald Trump says or does with a guy like Mark Kirk who has been a centrist Republican,” he said.

Still, it’s not likely that Kirk will stump with Trump, Brady said.

“I would guess that you don’t see Donald Trump in the same county as Sen. Kirk.”

Trump’s campaign sees his candidacy as a positive for the Republican Party.

Campaign Manager Corey Lewandowski framed Trump’s bid as about engaging those who haven’t ever been politically engaged. He told a story about a New Hampshire man in a wheelchair who asked a town clerk to come to his home so that he can register to vote for Trump.

“This election is about the silent majority, it is about all those people who felt that they haven’t been able to participate in the process,” Lewandowski said.

“That helps not just presidential race, it helps every race at every level of government from Senate to the local levels of government.”

In the end, most Republicans dismissed the notion that Trump would become the GOP nominee, despite his lead in the polls. But if he can, experts say they’d have to throw the playbook about the down-ballot races out the window.

“The assumption has been that there’s no way he can be the nominee. But I don’t know if that’s beginning to fray,” said University of Florida Political Science Professor Stephen Craig.

“If he manages to win the nomination, all of our traditional assumptions will be upset and we will be on such new turf that anyone that says they can predict the future should be put out to pasture.”