ABC News March 5, 2024

Sen. Kyrsten Sinema announces she won't run for reelection

WATCH: Sen. Kyrsten Sinema announces she will not seek reelection

Arizona's Kyrsten Sinema announced Tuesday that she is not running for reelection and will leave the Senate at the end of the year.

Sinema was elected in 2018 as a Democrat but left the party to become an independent in 2022.

In her video announcement, Sinema touted her moderate, middle-of-the-road outlook but said Americans have chosen to "retreat further to their partisan corners."

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

Sinema, who hadn't announced her 2024 plans, was being challenged on the left by Democratic Rep. Ruben Gallego and on the right by Republican Kari Lake.

Gallego released a statement Tuesday thanking Sinema for her years representing Arizona though quickly turned his attention to Lake, a staunch ally of former President Donald Trump and election denier who lost the governor's race to Democrat Katie Hobbs in 2022.

"As we look ahead, Arizona is at a crossroads. Protecting abortion access, tackling housing affordability, securing our water supply, defending our democracy -- all of this and more is on the line," Gallego said. "That's why Democrats, Independents, and Republicans alike are coming together and rejecting Kari Lake and her dangerous positions. I welcome all Arizonans, including Senator Sinema, to join me in that mission."

Sinema had been outraised every quarter last year by Gallego, and faced competition from Lake in courting the Republican donors. Polls showed Sinema running third in a hypothetical matchup.

"We may not agree on everything, but I know she shares my love for Arizona," Lake said in response to Sinema's announcement. Lake added: "Arizonans will not be fooled by Gallego. I will be a voice for all Arizonans."

Tom Brenner/Reuters, FILE
Senator Kyrsten Sinema walks to an elevator outside the Senate Chamber during a vote on Capitol Hill in Washington, May 19, 2022.

Sinema previously served three terms in the U.S. House and announced her first bid for the U.S. Senate in Sept. 2017, beating Republican Martha McSally for an open seat after Republican Sen. Jeff Flake declined to run again.

At times, Sinema was a thorn in the Democratic Party's side when it came to some aspects of President Joe Biden's sweeping agenda like drug pricing reform and scrapping the Senate filibuster as a way to codify abortion protections.

But she's been the heart of some of the most significant compromise legislation of the Biden presidency, including the infrastructure bill and the bipartisan gun safety bill.

MORE: Sen. Kyrsten Sinema leaving Democratic Party

More recently, she was a key negotiator on a bipartisan measure to tackle immigration policy and foreign aid, which was tanked by congressional Republicans under pressure from Trump.

"We appreciated her efforts on that," White House press secretary Karine Jean-Pierre said as she reacted in real-time to Sinema's announcement from the briefing podium. "And there are some other, obviously, ways that we've worked closely with her ... This is the first time I'm hearing the news. But she's been a partner with us on many critical issues that matter to the American people."

In announcing she will be leaving the Senate, Sinema said Tuesday that "compromise" has turned into a "dirty word."

"In 2017, I warned we were at a crossroads. Our democracy was weakened by government dysfunction and the constant pull to the extremes by both political parties," she said. "I promised I would do my best to fix it ... Through listening, understanding and compromise we delivered tangible results that make America safer, stronger and more prosperous."

She continued, "These solutions are considered failures either because they're too much or not nearly enough. It's all or nothing. The outcome less important than beating the other guy."