A blistering war for control of the Senate is taking place in high-stakes battles playing out in swing states across the country from Pennsylvania to Arizona. 

As Vice President Harris and former President Trump duke it out for control of the White House, the tug-of-war for Senate supremacy is largely coming down to seats that Democrats have held under razor-thin majorities the past three years. 

The retirement of Sen. Joe Manchin (I-W.Va.) has essentially guaranteed a notch for Republicans in the ruby red state. Democrats, backed by Manchin and three other independents, currently have a 51-49 advantage in the chamber. 

The GOP is also making a play for openings in Arizona, where Sen. Kyrsten Sinema, a Democrat-turned-independent like Manchin, is stepping down, and Michigan, where Sen. Debbie Stabenow (D) chose retirement rather than another run, too. 

Republicans additionally are putting up a fight against vulnerable Democratic incumbents. 

The vice president, representing whichever party wins the White House, would be the tiebreaker if the Senate splits 50-50 and determine which party controls the chamber. 

The nonpartisan Cook Political Report has ranked three Democratic-held seats as toss-ups this election cycle. Here are those and two other races to watch: 

Ohio 

Incumbent Sen. Sherrod Brown (D-Ohio) is in a fight for his political future, as he faces Trump-backed businessman Republican Bernie Moreno in a state that has trended redder in recent years. 

Now-vice presidential candidate JD Vance (R) trounced Democratic rival Tim Ryan in the Buckeye State’s last Senate race just two years ago. The Ohio GOP also holds a state government trifecta, controlling the governor’s office and both chambers of the Legislature. 

Cook lists the seat as a “toss up,” and The Hill/Decision Desk HQ’s polling analysis puts Brown with a slight lead as he fights for a fourth term. 

Montana 

Incumbent Sen. Jon Tester (D-Mont.) is also trying to fend off a Trump-backed Republican challenger in an increasingly red state as he seeks a fourth term. 

Trump, who has thrown his support behind Republican businessman Tim Sheehy, won the state by 16 points in 2020. 

Cook has rated the Montana race as a “toss up,” and The Hill/Decision Desk HQ polling analysis shows Sheehy ahead as he tries to unseat Tester. 

Michigan 

Stabenow’s retirement has put the Great Lakes State into play, with Cook listing the race as a “toss up.” 

Democratic Rep. Elissa Slotkin faces Trump-backed Republican Mike Rogers in the race playing out in the crucial swing state that has drawn significant campaign attention from Harris and Trump. 

Slotkin has held a slight edge over Rogers since the general election campaign kicked off earlier this year, polls reviewed by The Hill/Decision Desk HQ show. President Biden narrowly won the state four years ago. 

Arizona 

Progressive Rep. Ruben Gallego faces conservative firebrand Kari Lake in the race to replace Sinema in the Grand Canyon State. 

Lake, a MAGA Republican, unsuccessfully ran for governor two years ago, losing to Democrat Katie Hobbs 49.6 percent to 50.3 percent. Lake has been a prominent election denier and steadfast Trump supporter since that race. 

Sinema was elected the state’s first Democratic senator in nearly three decades with her 2018 win and before she switched parties. Sen. Mark Kelly (D-Ariz.) won the state’s other seat in a special election in 2020 and regular election in 2022. 

Cook has rated the Arizona opening as “leans Democratic” this cycle, and polling shows Gallego with a strong lead at this point in the campaign, according to The Hill/Decision Desk HQ analysis. 

Pennsylvania 

Republican businessman David McCormick is again battling for a Senate seat, after losing the GOP primary to Mehmet Oz by fewer than 1,000 votes two years ago and missing out on the chance to face John Fetterman (D-Pa.) in the general election. Fetterman defeated Oz in the end. 

This time, McCormick, with Trump’s backing, faces three-term incumbent Sen. Bob Casey (D) in the general election. 

Cook has rated the Keystone State, which has become a major focus of Trump and Harris’s campaigns, as “leans Democratic” in the Senate race, and The Hill/Decision Desk HQ analysis shows Casey ahead in the latest polls. 

BONUS: Be sure to also keep an eye on races in Maryland, Nevada and Wisconsin.