Independent Senator Kyrsten Sinema has made the decision not to seek re-election this year, bringing an end to her one-term tenure in the Senate. Sinema, who played a pivotal role in shaping legislation and negotiating compromises in the closely divided Senate, made the announcement via a video posted on her social media account.

In her video message, Sinema expressed her commitment to civility, understanding, and working together to accomplish tasks but noted that partisan conflicts have come to dominate the political scene. She believes her approach may not align with the current desires of the American public.

Sinema's departure sets the stage for a competitive and costly battle for her Senate seat. However, the race is expected to be less complex than a potential three-way contest if she had chosen to run again. The leading Republican candidate, Kari Lake, who is also running for governor in 2022, and the leading Democrat, Rep. Ruben Gallego, have already begun their campaigns to replace Sinema.

Polling for the race has been limited, but previous surveys consistently showed Sinema trailing behind both Gallego and Lake in a hypothetical three-way contest. The impact of her departure on the allocation of support between the two major candidates is uncertain.

Interestingly, Sinema believed she had stronger support among Arizona Republicans than within her former party. Last September, she outlined her path to victory, aiming to attract 10% to 20% of Democrats, 60% to 70% of independents, and 25% to 35% of Republicans.

Upon hearing the news, Rep. Ruben Gallego praised Sinema and invited her, along with all Arizonans, to join him in tackling important issues such as protecting abortion access, addressing housing affordability, securing the water supply, and defending democracy.

Republicans, hoping to regain control of the Senate, have identified Arizona as a potential pickup opportunity. With Democrats holding a slim majority in the Senate, the GOP needs to gain two seats to obtain a majority or one seat plus the tie-breaking vice presidency.

Sinema's political journey has been remarkable, from her early days as a Green Party organizer to becoming a favorite Democrat for the GOP in the U.S. Senate. She ran as a Democrat and won a seat in the Arizona Legislature in 2004, before being elected to the U.S. House in 2012. Sinema's moderate approach helped break the Democrats' losing streak in statewide elections when she was elected to the Senate in 2018.

During her tenure, Sinema played a crucial role in advancing President Biden's agenda in the closely divided Senate. She used her influence to shape significant legislation, such as the Inflation Reduction Act, and managed to remove provisions she opposed, such as tax rate increases for corporations and the wealthy. Sinema also led successful bipartisan negotiations on critical issues, including infrastructure and gun safety.

However, Sinema's relationship with Arizona Democrats deteriorated over time, leading her to leave the party and become an independent in 2022. This decision generated criticism and resulted in the loss of support from key allies, including EMILY's List.

Sinema's influence has waned with the Republican takeover of the House and Democrats gaining only one Senate seat in 2023. She had recently negotiated a border security deal, which was ultimately blocked by Republicans.

Arizona's status as a battleground state was reinforced in 2020 when President Biden narrowly won the state. In 2022, Senator Mark Kelly, a Democrat, secured re-election with a 5-point margin, while now-Governor Katie Hobbs, also a Democrat, narrowly defeated Kari Lake by less than 1 point in another statewide race.

Aside from Arizona, other key battleground races for the 2024 election include the re-election campaigns of Democratic Senators Jon Tester of Montana and Sherrod Brown of Ohio. In West Virginia, Democratic Senator Joe Manchin has announced that he will not seek another term.

With Sinema's departure, the race for the Arizona Senate seat becomes critical for both Republicans and Democrats, as it could potentially shift the balance of power in the Senate.