Pro-Trump Sheriff Mark Lamb is running for U.S. Senate in Arizona

Pinal County Sheriff Mark Lamb announced he's running for U.S. Senate in Arizona, becoming the first GOP candidate to hop in the race.

State of play: Democratic U.S. Rep. Ruben Gallego is also running for the seat currently held by Kyrsten Sinema, who announced earlier this year she was leaving the Democratic Party to become an independent.

• Sinema has not yet said whether she'll seek re-election.

Why it matters: This contest is expected to be one of the most competitive in the country and could determine which party controls the U.S. Senate.

What he's saying: Lamb's announcement video focused on cracking down on migrants crossing the southern border, and he promised to "stand up to the woke left and the weak politicians in Washington" to secure the border.

• "I have personally carried the dead bodies from the ditches, rescued children from sex trafficking and arrested gang members and drug dealers," he said.
• In the ad, Lamb stressed his support for gun rights and shared his anti-abortion position.

Between the lines: Lamb also spoke in the video about his son and granddaughter who died late last year in a car accident.

• He said his son struggled with fentanyl abuse throughout his life.
• "I know what deadly drugs and the criminals peddling them are doing to families and communities. I know what it did to my family," he said.

Flashback: Lamb was a supporter of former President Trump and has repeated many of his unsubstantiated claims of voter fraud.

• "We will not let happen what happened in 2020," Lamb said at a Prescott rally with Trump and other candidates last year, adding he partnered with conservative organization True the Vote to enforce election laws.

What's next: Other rumored GOP Senate candidates include:

• Kari Lake, the former TV anchor who lost the governor's race to Katie Hobbs;
• Blake Masters, the venture capitalist who lost the Senate race to Mark Kelly;
• Business leader Karrin Taylor Robson, who lost the GOP gubernatorial primary last summer to Lake.