Expectations of a record turnout has some Texas Republicans on edge that a handful of U.S. House incumbents may be in tougher fights than usual.

Republican consultants are projecting the presidential primary will drive turnout for their party's primary to the highest levels in decades. And many of those Republican voters are expected to be first-time voters, drawn to the campaign by anti-establishment figures like real estate magnate Donald Trump and U.S. Sen. Ted Cruz.

The question looming over the next 24 hours is whether those voters only weigh in on the presidential race or continue on down the ballot and vote against sitting members of Congress.

Four Republican incumbents, in particular, are the subject of the strongest interest among Republican operatives: U.S. Reps. Kevin Brady of The Woodlands, John Culberson of Houston, Pete Sessions of Dallas and Lamar Smith of San Antonio. 

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A key point to consider: All four of these incumbents have powerful committee assignments in Washington. A loss in a runoff may serve as a boon for base conservatives but would decrease the state’s legislative clout. 

None of these Republicans is expected to lose outright on Tuesday. In fact, all four could end up breezing past their rivals and onto re-election. 

But they could also be kicked to a dreaded runoff on May 24 if they fail to draw a majority of the vote. Whether or not a runoff, where turning out voters can be tougher, translates to mortal electoral danger for these incumbents has become a point of speculative debate among Texas political observers.

Here are races to watch Tuesday night: 

U.S. Rep. Kevin Brady

It would be a brutal twist of fate for Brady to struggle for re-election this year.

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Brady spent years working toward the chairmanship of the House Ways and Means Committee, an accomplishment he only achieved in November. But no other Texas Republican appears to be in more primary trouble than him.  

Last cycle, he trounced his nearest primary rival, drawing 68 percent of the vote in the state's 8th Congressional District, and since ascending to the chairmanship, he’s managed to raise eye-popping amounts for his campaign fund.  

His most organized rival, former state Rep. Steve Toth, has put in lackluster fundraising reports. Retired Lieutenant Colonel Andre Dean and his fellow veteran Craig McMichael, who ran against Brady in 2014, are also on the primary ballot.

But Brady is in enough trouble that outside groups - including the leadership-aligned Congressional Leadership Fund super PAC - are spending big to protect him. 

Under the same circumstances just four years earlier, Brady would seem safe. But the surprise 2014 primary defeat of former U.S. House Majority Leader Eric Cantor of Virginia rewrote the rules of incumbent survival.  

U.S. Rep. John Culberson

Culberson, who ran unopposed in his 2014 primary, spent most of the last year posting weak fundraising numbers. Which is the main reason so many Texas political insiders wonder if he is in electoral trouble. 

His seat on the House Appropriations Committee is a major asset to the delegation and to the state's 7th Congressional District, based in Houston. 

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Culberson's most organized rival is attorney James Lloyd, who is well-connected politically. But many consultants say his fundraising was not strong enough to boost his name identification in a prohibitively expensive media market. Also running for the party's nod is Maria Espinoza, National Director of the Remembrance Project, which highlights Americans who have been killed by people in the country illegally. 

Some inside the Culberson camp say they’re confident he will clear the runoff, while outsiders smell danger for the eight-term congressman.

U.S. Rep. Lamar Smith

Smith, who chairs the House Committee on Science, Space and Technology, has maintained a robust campaign operation since the beginning of this election cycle. Most consultants predict he is well situated to avoid a runoff. 

That said, he faces a rematch against businessman Matt McCall, who won 34 percent of the vote in the state's 21st Congressional District to Smith’s 61 percent in 2014. 

The field is crowded — with McCall, software engineer John Murphy and businessman Todd Phelps on the ballot— but Smith dwarfs his rivals in fundraising. The troublesome scenario a handful of Republican operatives game out for Smith is that the other three candidates win enough of the vote to push him below 50 percent and into a runoff.

U.S. Rep. Pete Sessions

Sessions’ challenger, businessman Russ Ramsland, is running a better-funded and more organized campaign than the incumbent’s 2014 rival, activist Katrina Pierson. In that race, Sessions bested Pierson, now Trump’s spokeswoman, with 64 percent of the vote in the state's 32nd Congressional District. This year, three other candidates on the ballot — veteran Paul Brown and Cherie Myint Roughneen, a nurse, and Jeff Tokar — could make it tougher for Sessions to clear 50 percent of the vote.

But while Sessions is a perennial target, most in the GOP consultant world are shrugging off this challenge because of the sheer money Sessions is spending — well over $1 million — in the expensive Dallas-Fort Worth media market.