Arizona Sheriff Mark Lamb running for US Senate seat held by Sinema

Pinal County Sheriff Mark Lamb has filed paperwork to run for U.S. Senate in Arizona, becoming the first Republican to step forward to challenge incumbent Sen. Kyrsten Sinema, an independent.

Lamb declared his candidacy Monday in a statement filed to the Federal Elections Commission. An outspoken critic of President Biden's immigration policies, Lamb has also earned recognition in Arizona and nationally for his opposition to the federal COVID-19 vaccine mandate in 2021 and staunch support for former President Donald Trump. 

Arizona's Senate race will be hotly contested in 2024. Republicans need to win two seats to flip the Democratic Party's current 51-49 majority, with Sinema and Sen. Angus King, I-Maine, caucusing with Democrats. The 2024 Senate map is generally believed to favor Republicans, as Democrats from three states Trump won in 2020 are up for re-election. 

Sinema, who left the Democratic Party in December after her relationship with many members of the party ruptured, is raising money for a potential re-election campaign but has not said whether she will seek a second term. U.S. Rep. Ruben Gallego is the only Democrat in the race. He said last week he raised $3.7 million in the first quarter.

SHERIFF MARK LAMB CALLS OUT ‘ATTACK ON TRADITIONAL VALUES’ IN AMERICA, HAS A FIX FOR THAT

Lamb was sworn in as Sheriff of Pinal County on Jan. 1, 2017. He oversees a county that is roughly the size of Connecticut and manages more than 650 employees within the department.

Before becoming sheriff, Lamb trained with the Maricopa County Sheriff's Office Deputy Academy and was named Valedictorian of his class. He was hired by the Salt River Pima-Maricopa Indian Community, and worked hard and was named Rookie of the Year. The next year, he received an Officer of the Year award. He was later promoted to Detective on the Gang Enforcement Unit and in his first year in that position was named Detective of the Year. 

SHERIFF MARK LAMB OF ARIZONA HAS A STERN MESSAGE FOR BIDEN AT THE BORDER: ‘APOLOGIZE’ FIRST

As sheriff, Lamb has made combating drug trafficking and smuggling top priorities for his department. While Pinal County is not a border county, it acts as a "pass through" county for drug and human trafficking routes. Earlier this year, ahead of Biden's visit to the southern border, demanded that the president "apologize to the American people." 

"I think this administration has been disrespectful to our Border agents because they haven't had their backs," Lamb told Fox News Digital in January. 

ARIZONA GOP SENATE LEADER SAYS KARI LAKE'S EXPECTED US SENATE ANNOUNCEMENT WON'T DETER HIM FROM RUNNING

"They haven't appropriately staffed them. They've had them doing jobs that they weren't designed to do. And they continue to show no outward support for them."

The 2024 Arizona Senate primary could be a crowded affair, with several high-profile Republicans considering bids. 2020 GOP gubernatorial candidate Kari Lake would be the front-runner if she steps in, as she remains popular with Republican voters even though she lost to Democratic Gov. Katie Hobbs by more than 17,000 votes in November. Unsuccessful Senate candidate Blake Masters, and failed gubernatorial and senate candidates Jim Lamon and Karrin Taylor Robson are also considering running for Senate. 

CLICK HERE TO GET THE FOX NEWS APP

Lamb's viability in a large field will come down to his as-of-yet undemonstrated ability to raise money against several opponents with previous experience running statewide campaigns and much higher name recognition. 

Lamb experienced tragedy late last year, when his 22-year-old son, the son’s fiancée and their 1-year-old daughter were killed in a crash when their vehicle was hit by a suspected drunken driver.

The Associated Press contributed to this report.