Republican Kari Lake, who lost the race for Arizona governor last year to Democrat Katie Hobbs, filed the papers to run for the Senate on Monday.
The seat is held by Kyrsten Sinema, a Democrat-turned-independent who hasn’t said yet whether she will run for re-election.
On Tuesday, she put up a social media post teasing a bit announcement coming in a week.
Lake, 53, a former TV anchor, lost last year’s governor’s race by 17,117 votes after she ran a campaign in the mold of former President Donald Trump’s — replete with election conspiracy theories and hyperbolic claims about an immigrant "invasion" that was robbing Americans of jobs.
She has spent nearly a year challenging her loss in court and raising money over rigged election claims. She repeatedly and falsely claimed for months she would be soon be made governor.
In May, a state judge rejected her last remaining attempt to overturn the results of the election, ruling that there wasn’t evidence of misconduct in Maricopa County’s signature-verification process and that the alleged misconduct hadn’t affected the outcome of the election anyway. Lake appealed the ruling in September.
In July, some of her lawyers were sanctioned $122,200 for filing what a federal court said was a "frivolous" election lawsuit.
And in late September, Lake went to court for her third election trial, at which she is seeking access to ballot envelope signatures in Maricopa County. Lake has argued that the county didn't properly check voters' signatures on the ballot envelopes against the on-file signatures, ignoring fraudulent votes she argues cost her the election.
Still, on social media in recent months, Lake's rhetoric has included discussion of border security and abortion, as well as criticism of Sinema and President Joe Biden.
Lake will go up against Pinal County Sheriff Mark Lamb in the GOP primary.
Rep. Ruben Gallego, D-Ariz., is also running for Sinema’s seat from the left, boasting a progressive agenda.
Though Sinema hasn't yet announced her re-election plans, privately her political team has been mapping out a campaign strategy and pitching donors, according to a document obtained exclusively by NBC News.
Arizona is expected to be a key battleground state in the general election. Biden narrowly won it in 2020, a victory that was challenged by Trump, who is running again for the GOP presidential nomination.