(NEXSTAR) — The battle for the Senate is anyone’s ballgame with only a week to go until voters head to the polls.

Republicans, needing to net only one seat, are knocking on the door as the national environment moves increasingly in their direction and some surveys show them in the lead in both Georgia and Nevada. According to FiveThirtyEight’s latest projections, the fight for the majority is a “dead heat,” turning the final days into an all-out sprint to get voters out to the polls. 

Here are five races that will determine the Senate majority.

Arizona 

Of the five states on this list, Democrats still have the best chance of holding Sen. Mark Kelly’s seat, though Republican Blake Masters has closed the gap in recent weeks.

Kelly, long considered one of the best Senate Democratic incumbents up for reelection, held a sizable lead over Masters for nearly two months after the GOP nominee emerged from the early August primary. Much of that was thanks to the onslaught of ads as a result of the Democrat’s juggernaut fundraising operation.

But the script has flipped in recent weeks, with Masters cutting Kelly’s lead to near the margin of error in most surveys. Much of that is due to two reasons, according to strategists: the natural tightening of the race in a swing state, and the impact of Republican Kari Lake’s presence at the top of the ticket. 

“I think Kelly squeaks it out, but it’s way tighter than anybody would want,” said one Democratic operative involved in Senate races. 

One Arizona-based GOP operative told The Hill that a The New York Times-Siena poll that emerged on Monday is “realistic,” but added that a 2- to-3-point undercount for Masters at this point is entirely plausible, with Lake being the driving force behind a possible upset. 

“There’s definitely a strategy of Lake and Masters working together,” the strategist said. “She’s trying to pull the whole team across the finish line.” 

According to the latest RealClearPolitics average, Lake leads Arizona Secretary of State Katie Hobbs (D) by 3.8 percentage points. Similarly, Kelly tops Masters by 2.4 percentage points.

Georgia

Sen. Raphael Warnock (D-Ga.) once appeared to have a distinct edge over his Republican opponent Herschel Walker, a former NFL star and first-time candidate who has grappled with a slew of personal and professional controversies over the course of his Senate campaign. 

Perhaps one of the most eye-popping revelations about Walker came early last month when the Daily Beast published a story detailing allegations that Walker had paid for his then-girlfriend to have an abortion in 2009.

Yet Walker hasn’t taken much of a hit in the polls. He has hammered Warnock repeatedly on perceived rising crime and lingering economic concerns, while largely brushing off the allegations as lies. In turn, he’s steadily narrowed his polling gap with Warnock, who now leads in the race by little more than 1 percentage point, according to FiveThirtyEight’s polling average.

“The fact of the matter is he’s been fired at as much as I’ve ever seen,” said Chuck Clay, a former state senator and Georgia GOP chair. “Unless there’s some other lurking horror story out there we’re not aware of, I think he’s been pretty well raked over the coals.”

What makes the race between Warnock and Walker particularly volatile is the fact that Georgia is one of only two states where candidates are required to receive more than 50 percent of the vote to win their election. And as of now, neither Warnock nor Walker are hitting that threshold.

“Maybe [Walker’s] not at 50 percent, but it doesn’t appear all the negatives have had a significant impact,” Clay said. “It’s all going to come down to that final 2 or 3 percent of people who are still on the fence.”

Nevada

Of all the Senate Democrats locked in ever-tightening reelection bids, Sen. Catherine Cortez Masto (D-Nev.) might be the most vulnerable.

Even in Democrats’ brightest days of the campaign, she’s never held the kind of clear lead over her Republican rival, former state Attorney General Adam Laxalt, that other battleground state Democrats have. A new poll from The New York Times and Siena College released on Monday found Cortez Masto and Laxalt deadlocked at 47 percent apiece. 

Nevada poses a series of challenges for both parties. On one hand, Democrats have had a winning streak in the state in recent years, culminating with the ouster of former Sen. Dean Heller (R-Nev.) in 2018 and President Biden’s victory there two years later.

On the other hand, Republicans’ improving margins among Latino voters could chip away at a base of support that Democrats have long relied on to propel their victories in Nevada. The state also has a transient population that makes it particularly hard to pin down politically.

“I think, in a lot of ways, Nevada has just been kind of hard to get a hold on,” said one Democratic strategist who has worked on Senate campaigns. “It’s kind of a meeting point for a lot of the crosscurrents and trends we’ve been seeing.”

Pennsylvania

The wind is firmly at the back of Mehmet Oz in the final week of the campaign, but it remains to be seen whether that will be enough for him to defeat Lt. Gov. John Fetterman (D) next week. 

The trend lines are clearly in Oz’s favor at this stage. His constant attacks on crime have resonated with voters for months and he was the beneficiary of Fetterman’s continued struggles during last week’s debate due to his stroke. 

However, Oz’s push in the late stages hinges on whether he can peel off enough supporters of state Attorney General Josh Shapiro (D) in the gubernatorial race, particularly in the Philadelphia suburbs. Shapiro is considered the heavy favorite against state Sen. Doug Mastriano (R) to replace Gov. Tom Wolf (D), who is term-limited.

“That crossover group in a really tight race could be impactful,” said Chris Borick, a political science professor at Muhlenberg College, who laid out Oz’s recent message. “It’s ‘beat up Fetterman and sell yourself as moderate.’ He’s not talking about Trump. He’s not talking about any lightning-rod partisan stuff like Mastriano.”

“It’s an appeal,” Borick continued. “His pitch to those folks is that he’s OK. That he’s not radical.”

Fetterman still leads by 1.5 percentage points, according to the latest RealClearPolitics average of surveys. 

No matter who emerges victorious, the winner is likely to win by a slim margin, increasing the likelihood that a winner will not be known on election night and that it could take days to determine who will be the next senator. Acting Secretary of State Leigh Chapman (D) said last week that churning out full results could “take at least a few days.”

“If this is a tight election, we’re going to go down a very dangerous rabbit hole again where legitimacy of the election is called into question,” one Pennsylvania-based GOP operative told The Hill. “When you see other states that get this stuff done on time, it calls into question why Pennsylvania is unable to.”

Wisconsin

Despite facing a tough political environment in 2022 overall, Democrats eyed Wisconsin eagerly, believing that voters just might be convinced to oust their controversy-prone Republican incumbent, Sen. Ron Johnson (R-Wis.). 

They nominated Lt. Gov. Mandela Barnes (D-Wis.) for the job following a long and occasionally bitter primary campaign. And while early polls suggested that Johnson was in danger, Barnes also struggled to get his general election bid off the ground, opening himself up to weeks of attacks casting him as a “radical leftist.”

Democrats have been pouring cash into the race in its final weeks, hoping to give Barnes a last-minute boost. Former President Obama, still one of the most popular Democrats in the country, swung through Wisconsin over the weekend in an effort to salvage his party’s chances there.

And to be sure, the race remains close, with Johnson holding a 3.4-point advantage over Barnes in FiveThirtyEight’s average of the race. Still, Republicans argue that Barnes’s prospects were overplayed and that Democrats underestimated Johnson’s strength.

Doug Heye, a Republican strategist, echoed Senate Minority Leader Mitch McConnell (R-Ky.), who earlier this year downplayed his party’s prospects of winning the Senate because of “candidate quality.”

“Some people tried to give McConnell flack for saying that candidate quality matters. But it also matters on the Democratic side,” Heye said. “It’s part of why Mandela Barnes has been such a letdown.”