Sinema has not yet said whether she’ll run for reelection, but a three-way general election clash with Gallego and a to-be-determined Republican candidate could become one of the most high-profile races across the country. No Republican has yet announced a bid to unseat Sinema, though top contenders include former gubernatorial candidate Kari Lake and former Senate candidate Blake Masters.

Other Democrats, meanwhile, have passed on potential Senate campaigns. Last week, Rep. Greg Stanton became the latest to forgo a bid of his own, though Tucson Mayor Regina Romero is still getting buzz as another potential Democratic candidate.

Gallego, a 43-year-old former Marine who served in Iraq, would be Arizona’s first Latino senator if elected. He announced his candidacy with a video that featured him talking to veterans at an American Legion post in Guadalupe, Ariz.

“You’re the first group of people that are hearing this besides my family. I will be challenging Kyrsten Sinema for the United States Senate, and I need all of your support,” Gallego said in the video.

Gallego’s campaign will force the Democratic Senatorial Campaign Committee and others in the party to choose whether or not to defend Sinema as an incumbent. Though she’s opposed key portions of the White House’s agenda, Sinema has largely voted in favor of most Democratic legislation and to confirm President Joe Biden’s nominees.