Mark Kelly, the former astronaut and gun-control activist who is married to Gabrielle Giffords, announced on Tuesday that he would run for Senate in Arizona, challenging appointed Senator Martha McSally and intensifying the Democratic threat to Republicans’ narrow control of the chamber.
Mr. Kelly’s entry sets up a possible general election between two combat veterans in a swiftly changing state, and may elevate Arizona further as a 2020 battleground. Both parties already view Arizona as a swing state in the presidential race and in 2018 Democrats won a Senate race there for the first time in decades.
Ms. McSally, an Air Force veteran, was narrowly defeated in a statewide race last year by Senator Kyrsten Sinema. Ms. McSally joined the Senate anyway a few months later, appointed to fill the vacancy left by John McCain’s death after a placeholder appointee, Jon Kyl, resigned.
[Make sense of the people, issues and ideas shaping American politics with our newsletter.]
Mr. Kelly, 54, unveiled his campaign in an online video highlighting his experience as an astronaut and Navy pilot. Ms. Giffords, a former member of Congress who was shot and nearly killed by a deranged gunman in 2011, appeared beside him in the message.
Ms. Giffords was seen as a likely future Senate candidate before the shooting, and the video casts Mr. Kelly as carrying forward her legacy. For several years, the two have led a national gun-control group that played a significant role in the midterm elections.
Narrating the video, Mr. Kelly presented himself as a non-politician and a unifying figure, focused on issues like health care, wage stagnation and climate change. That approach echoes the avowedly moderate course Ms. Sinema charted in her campaign last year, when she successfully assembled a coalition of young people, Latinos and centrist whites opposed to President Trump.
“Solving some of the hardest problems requires one thing, and that’s teamwork,” Mr. Kelly said in the video. “Partisanship and polarization and gerrymandering and corporate money have ruined our politics, and it’s divided us.”
Mr. Kelly lamented a “retreat from science and data and facts” that he said prevents problems from getting solved. He did not mention Mr. Trump or attack the Republican Party.
Mr. Kelly may not have an open path to the Democratic nomination. At least one other prominent Democrat, Representative Ruben Gallego, has been exploring the race. He could present a challenge to Mr. Kelly on the left.
Mr. Gallego said on Tuesday morning that he was still considering the race, indicating he would not make way for Mr. Kelly.
“I’ve made no secret of the fact that I’m looking seriously at running for the U.S. Senate in 2020, and that hasn’t changed,” Mr. Gallego said on Twitter. “I’ll be making a final decision and announcement soon.”
Ms. McSally is also likely to face pressure from her party’s activist flank. In 2018, she shifted well to the right to navigate a Republican primary, aligning herself closely with Mr. Trump in a way that ultimately harmed her in the general election.
The Arizona race is one of a handful that will decide control of the Senate in 2020. Republicans have a 53-seat majority in the chamber, meaning that Democrats need to gain three or four seats to take power, depending on which party holds the vice presidency.
The two parties are also aggressively targeting Republican-held Senate seats in Georgia, Iowa, Maine, Colorado and North Carolina, and a Democratic-held seat in Alabama, among others.
Mr. Kelly has been among the most closely watched potential Democratic candidates, along with Stacey Abrams in Georgia.