Republicans were hoping for a viable GOP candidate to win the contest by a plurality with Sinema and Democratic candidate Rep. Ruben Gallego splitting the ticket, but talk of Masters and Lake considering their own runs is sparking concern.

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"Any candidate in ’24 that has, as their principal campaign theme, a stolen election, is probably going to have the same issues that some of the ’22 candidates had," Sen. John Thune, the Senate GOP’s No. 2 leader, told Politico. "I just don’t think that’s where the American public is. It’s a swing state — we need to have a good Republican nominee, obviously. You know, whoever gets in, I hope they focus on the future, not the past."

Lake is also rumored to be considering a potential run for Sinema's seat, but a final determination likely will not come until Lake's election lawsuit is exhausted, according to multiple reports. The MAGA firebrand lost her gubernatorial campaign by less than one point to then-Secretary of State Katie Hobbs. 

Already in the 2024 race for Arizona's Senate seat is Gallego, a longtime critic of Sinema's, who announced his campaign earlier this month. 

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Former Gov. Doug Ducey, the two-term Arizona governor, has been floated as a popular, traditional Republican choice for the seat, though Ducey turned down the opportunity to run for Sen. Mark Kelly's seat.

"He’s made it pretty clear he’s not interested, but he’d be a great option," Thune told Politico. 

The 2024 Senate map strongly favors Republicans, with multiple Democrats defending seats in GOP stronghold states — West Virginia, Montana and Ohio — to hold on to their 51-49 majority.