Republican Kari Lake filed paperwork Tuesday to run for Sen. Kyrsten Sinema’s (I) seat in Arizona, laying the groundwork for a potential three-way race in a critical swing state.

Lake, who previously ran for Arizona governor, registered her Senate campaign committee with the Federal Elections Commission a week ahead of her expected campaign launch.

The former news anchor lost to now-Gov. Katie Hobbs (D) last year, drawing attention as a Trump-aligned candidate who was among the party’s most prominent election deniers running for office. Lake has not accepted the results of the 2022 gubernatorial election.

While some polls have shown Lake leading Republicans in a hypothetical primary, her candidacy could prove more of a challenge in the November general election.

Pinal County Sheriff Mark Lamb (R) has already announced a run for Sinema’s seat, while Rep. Ruben Gallego (D-Ariz.) has launched a bid for the Democratic nomination. Former Arizona Senate candidate Blake Masters was reportedly weighing a run but has not made an unofficial announcement.

Throwing uncertainty into the race is Sinema’s plans. She changed her party affiliation from Democrat to independent late last year. Sinema is reportedly gearing up for a reelection bid, though she has not formally announced a campaign.

If Sinema does run, it’s unclear whether she’ll be able to prevail in a general election and whether she might peel away votes from Republicans or Democrats.