CNN
 — 

Mark Lamb, the sheriff of Pinal County, has filed paperwork to run for Senate in Arizona, entering the unpredictable three-way race for the seat currently held by independent Sen. Kyrsten Sinema.

Lamb is the first prominent Republican to formally join the primary, which could escalate further with the entry of Kari Lake, the far-right unsuccessful 2022 Arizona gubernatorial nominee who has also teased a bid.

Over the last few years, Lamb has worked to raise his profile with the GOP base, making regular appearances on Fox News, focusing on immigration and criticizing Covid-19 vaccine requirements.

Lamb also has a checkered history as a proponent of false claims about election integrity. He supported former President Donald Trump’s efforts to overturn the 2020 election, defended rioters at the Capitol on January 6, 2021 and vowed to investigate voter fraud in the 2022 midterms. However, at a congressional hearing earlier this year, Lamb admitted he had seen “zero evidence” of fraud that could have impacted the outcome in 2020.

Ahead of a potentially crowded and contentious primary, Lamb is viewed favorably by some top Republicans, GOP sources have told CNN. Meanwhile, Abe Hamadeh, formerly the Republican nominee for Arizona attorney general, is also weighing a run. Both Lamb and Hamadeh met recently with National Republican Senatorial Committee officials.

Two other Republicans, Jim Lamon and Karrin Taylor Robson – who ran in 2022 for Senate and governor respectively – are also considering jumping into the race, sources familiar with the matter say.

Trump’s influence looms large. His endorsement of Blake Masters in the 2022 race proved influential, and Lake has been loudly auditioning for his support as she’s traveled the country following her loss in the gubernatorial race.

In addition, Democratic Rep. Ruben Gallego announced in January that he will also challenge Sinema in 2024 after she declared she was leaving the Democratic Party late last year to register as an independent.

Gallego’s declaration sets up a three-way race in a battleground state that’s been the epicenter of election controversies in consecutive cycles. The race will also put pressure on national Democrats, who are attempting to retain a two-seat US Senate majority while defending several vulnerable incumbents across the country.

Sinema has not yet announced her plans for 2024, but The Wall Street Journal reported earlier this week that her team is preparing for reelection.