Republicans in the United States Senate are poised to hold their razor-thin majority, and possibly add to it by a few seats, boosted by the partisan spat over newly minted Supreme Court Justice Brett Kavanaugh.

Even as the Democratic Party is on the cusp of surfing a tide of suburban discontent with President Trump and taking power in the House of Representatives, a decidedly favorable map of battlegrounds that runs right through the heart of some of the most conservative states in America will protect Republican control of the Senate.

Senators serve six-year terms, and only about one third of the 100-seat chamber is contested every two years. This year, with the addition of special elections in Mississippi and Minnesota, there are 35 Senate seats on the ballot across the country. But only about two dozen of those are actually considered in play, with the remainder a solid bet to stand pat. Even among those considered competitive in some form, only about a dozen are worth watching as the Republicans attempt to pad their 51-49 majority.

The Democrats are running strong incumbents, such as Sens. Heidi Heitkamp of North Dakota and Claire McCaskill of Missouri, and compelling challengers, such as Rep. Beto O’Rourke of Texas and former Gov. Phil Bredesen of Tennessee.

But Trump is popular in these and other contested red states — and they reverted to their natural partisanship after the explosive Kavanaugh hearings and passionate protests over his nomination reached their apex earlier this month.

“Contrary to all the weather metaphors, Republicans are well-positioned to maintain their Senate majority and maybe even gain seats,” said Nathan Gonzales, publisher of Inside Elections, a nonpartisan political handicapper based in Washington.

Before the Kavanaugh confirmation process was rocked by allegations of sexual misconduct, O’Rourke was nipping at the heels of Republican Sen. Ted Cruz, threatening a Texas-sized upset in the Lone Star State. In Tennessee, Bredesen, a popular former governor, led Republican Rep. Marsha Blackburn in most polls even though Trump won there in 2016 by 26 percentage points. In North Dakota, Heitkamp trailed Republican Rep. Kevin Cramer, and in Missouri, McCaskill was in a toss-up race with Republican Josh Hawley, the state attorney general.

In nearly every survey of those contests conducted since the Kavanaugh controversy erupted in late September, the Republican candidate led, in some cases by a wide margin.

The kerfuffle has also brought some Senate races that Republicans had written off into play.

Senate Leadership Fund, the super PAC affiliated with Senate Majority Leader Mitch McConnell (R-Ky.), plans to advertise in Montana, reversing the group’s previous conclusion that Sen. Jon Tester (D-Mont.) was too entrenched to defeat.

And in Arizona, Republicans were resigned to Democratic Rep. Kyrsten Sinema winning the seat being vacated by Republican Sen. Jeff Flake. Now, Rep. Martha McSally, the Republican nominee, is surging.

But the Republicans in the Senate aren’t completely immune to the headwinds being fanned by the White House.

Sen. Dean Heller (R-Nev.) is embroiled in a tug of war with Democratic Rep. Jacky Rosen in a state Trump lost to Democratic presidential nominee Hillary Clinton two years ago. Heller has voted in line with his purple state, but could be sunk if the Las Vegas suburbs revolt and Nevada’s considerable population of Hispanics turn out in force.

In Michigan, Ohio, Pennsylvania and Wisconsin, four states Trump won, the Democratic incumbents appear on a glide path to re-election, even though in a few of those contests, the Republicans fielded strong candidates. Meanwhile, in West Virginia, probably the most pro-Trump state in the union, Democratic Sen. Joe Manchin appears headed for re-election. Manchin, it’s worth noting, was the only Democrat in the Senate to vote in favor of Kavanaugh’s confirmation.

North Dakota

Incumbent: Sen. Heidi Heitkamp (D) vs. Rep. Kevin Cramer (R)

RealClearPolitics average: Cramer +8.7%

Heitkamp always had an uphill climb in a state that delivered 63 percent of its vote to President Trump just two years ago and is still pleased with his leadership. The first-term centrist-minded Democrat seemed ahead of the game as the calendar passed Labor Day, putting Cramer on the defensive on trade, a major issue in a state that exports billions of dollars in agricultural commodities to China. The soybean harvest comes right around Election Day, and Beijing isn’t buying amid a trade dispute with Washington initiated by the White House. But the nasty fight over Supreme Court Justice Brett Kavanaugh appeared to foreclose any chance Heitkamp had of pulling off an upset. After she voted against his confirmation, citing uncorroborated sexual-assault allegations, her poll numbers plummeted.

Nevada

Incumbent: Sen. Dean Heller (R) vs. Rep. Jacky Rosen (D)

RealClearPolitics average: Heller +1.7%

Heller is among the few vulnerable Senate Republicans on the 2018 ballot. His purple state sided with Democrat Hillary Clinton over President Trump by about two points; the statewide vote is dominated by suburbs in Las Vegas and Reno; and Hispanics — a major component of the electorate — can, on occasion, be more active here than similar cohorts in other states. (Although Hispanic turnout is never as good as it could be in many states, the Democratic Party has done a good job of registering and activating this demographic in Nevada.)

These ingredients have spelled trouble for Republicans across the country in the midterm elections, and Heller is no exception. But the Republican, often underestimated, is hanging tough with Rosen, a first- term congresswoman who has underwhelmed voters in Nevada and failed to create separation between herself and the GOP incumbent. Heller barely won in 2012, but managed to do so even as President Barack Obama captured Nevada by 7 points. Look for another photo finish this year.

Missouri

Incumbent: Sen. Claire McCaskill (D) vs. state Attorney General Josh Hawley (R)

RealClearPolitics average: Hawley +0.4%

McCaskill shouldn’t have even won a second term in 2012. But after her opponent that year, Republican Todd Akin, uttered the term “legitimate rape” as part of a discussion about abortion, the bottom dropped out, as GOP voters in this ruby-red state grudgingly sided with the Democrat.

Hawley, a consensus conservative, has gifted McCaskill with no such gaffes. The contest has been a seesaw battle, but the senator’s personal favorable ratings always trailed behind her ballot position, a troubling sign. Momentum finally began to shift toward Hawley with the partisan battle to confirm Kavanaugh. Complacent conservatives awakened and engaged in the midterm campaign, tipping the scales in favor of the Show Me State’s more natural political inclinations, which enabled Trump to win here by 20 points.

Texas

Incumbent: Sen. Ted Cruz (R) vs. Rep. Beto O’Rourke (D)

RealClearPolitics average: Cruz +7%

Cruz had struggled for months. His image was still in the tank, a byproduct of his 2016 presidential bid and long-since-resolved feud with now-President Donald Trump. And, he had to deal with the avalanche of glowing profiles of O’Rourke. The Democrat has electrified grass-roots liberals, who have showered him with cash, an all-time record of $38.1 million in the third quarter of this year alone. The problem for O’Rourke is that the same charismatic progressivism that helped him raise all of that money is out of step with conservative Texas, where the GOP does better than the national average with Hispanics. The Republicans’ worries about Cruz’s prospects appear to have subsided as the confirmation battle to install Kavanaugh on the Supreme Court made this a contest of issues, not personality, shaking any thoughts the Lone Star State might have had about giving O’Rourke a shot.

Ohio

Incumbent: Sen. Sherrod Brown (D) vs. Rep. Jim Renacci (R)

RealClearPolitics average: Brown +16%

How do you know it’s a tough year for Republicans? Even as a favorable Senate map is poised to retain their majority from any blue-tide hits on Election Day, the race in Ohio has never been in question. Even though Trump won this quintessential swing state by nearly 10 points, Brown, a passionate liberal, has barely broken a sweat versus Renacci, the Republican that Trump personally recruited into the race. It helps that Brown has, over the years, forged a strong relationship with Ohio voters and tends to agree with Trump on trade. Perhaps because of Brown’s credibility with voters; perhaps because, in a tough year for Republicans, the state has reverted to its typically swingy status, Kavanaugh has not altered the dynamic in the Buckeye State. Look for Brown to cruise.

Tennessee

Open Seat: Rep. Marsha Blackburn (R) vs. former Gov. Phil Bredesen (D)

RealClearPolitics average: Blackburn +5.5%

Blackburn trailed for months against the more well-known Bredesen despite the state preferring President Trump over Democrat Hillary Clinton by a whopping 26 percentage points. It was a testament to Bredesen’s strength. A bona fide centrist, Bredesen exhibited legitimate crossover appeal with Republicans who fondly remembered his tenure in the governor’s mansion. Indeed, he was more appealing to the establishment-oriented GOP money-set at the outset of the race than was Blackburn, a doctrinaire conservative. But the row over Kavanaugh did something Blackburn had labored to do for months: It made the race in Tennessee a question of which party would control the Senate majority. Republican voters there were willing, maybe, to elect the governor they liked over the congresswoman they weren’t sure of, but not if it meant handing the keys to the Senate to Minority Leader Charles Schumer of New York. Blackburn has led in every poll since.

David Drucker is a Washington Examiner Senior Correspondent and CNN political analyst