Sen. Kyrsten Sinema (I-Ariz.) will not seek a second term, she announced Tuesday after more than a year of side-stepping questions about her political future.

Why it matters: Her exit clears the way for a likely matchup between Republican Kari Lake and Democratic Rep. Ruben Gallego in a contest that could determine control of the Senate.

• As Lake and Gallego ramped up their campaigns, it became increasingly clear that Sinema's path to victory was extremely narrow.
• Sinema won in 2018 as a Democrat, becoming the first non-Republican to win an Arizona Senate seat since 1988.

What they're saying: "The only political victories that matter these days are symbolic — attacking your opponents on cable news or social media. Compromise is a dirty word," Sinema said in a video announcing her retirement and lamenting the breakdown of bipartisanship.

• "I believe in my approach, but it's not what America wants right now," she continued.
• "Because I choose civility, understanding, listening, working together to get stuff done, I will leave the Senate at the end of this year."

Zoom in: During her first term, Sinema positioned herself as a moderate — often frustrating Democratic leadership who had to court her vote on the party's top progressive priorities.

• Her position as a centrist swing vote allowed her to play an outsized role in major legislation like the bipartisan infrastructure law, the Inflation Reduction Act and the $280 billion Chips and Science Act.
• When Sinema stood in the way of the Democratic attempt to repeal the filibuster in 2022, the Arizona Democratic Party censured her.
• In December 2022, she announced she would leave the Democratic Party and become an independent.

How it's playing: "With recent polling showing Kyrsten Sinema pulling far more Republican voters than Democrat voters, her decision to retire improves Kari Lake's opportunity to flip this seat," National Republican Senatorial Committee chair Steve Daines (R-Mont.) said in a statement.

• Gallego — who has been fiercely critical of Sinema since launching his campaign — thanked the senator for her service and called on her to help Democrats defeat Lake, a pro-Trump election denier.
• "Ruben Gallego would be a radical departure from the representation we have had in Arizona," Lake said in a statement praising Sinema for defending the filibuster.

Editor's note: This story has been corrected to reflect that a non-Republican last won an Arizona Senate seat in 1988, not 1994.