Arizona's Senate race just got a whole lot less interesting following Kyrsten Sinema's decision to retire

• Sen. Kyrsten Sinema announced on Tuesday that she wouldn't seek reelection.
• Arizona won't be the site of an epic three-way Senate race as many had predicted.
• Instead, it will be a head-to-head race between Rep. Ruben Gallego and Kari Lake.

Sen. Kyrsten Sinema is not running for reelection — denying the political world the opportunity to see what would've been one of the most fascinating Senate races in recent memory.

When the mercurial senator announced her decision to leave the Democratic Party at the end of 2022, many believed that it was a calculated political move to boost her chances of reelection, especially considering that she would remain a part of the Democratic majority in the Senate.

After all, she had angered most of her party over her opposition to aspects of President Joe Biden's domestic agenda and her resistance to changing the Senate's 60-vote filibuster rule. She was also likely to lose the Democratic primary to Rep. Ruben Gallego of Arizona.

Since then, Sinema had stubbornly refused to say whether she would seek reelection, even as her campaign touted the more than $10 million she had to spend.

Her announcement on Tuesday guarantees that the Arizona Senate race will feature a head-to-head matchup between Gallego and Kari Lake, a former broadcast journalist and staunch ally of former President Donald Trump who has refused to concede her loss in the 2022 gubernatorial race.

In other words, it will be a race that pits a progressive-leaning Democrat against a fire-breathing MAGA acolyte. Many such cases.

Sinema's exit may give Lake a bit more of an opening than she had before, given that polling showed that the independent senator drew much of her dwindling support from Republican voters in the state.

Sen. Steve Daines of Montana, the chair of Senate Republicans' campaign arm, said in a statement that Sinema's retirement "improves Kari Lake's opportunity to flip this seat."

Yet Lake couldn't pull it off in 2022, despite widespread perceptions that she was favored in that year's governor's race. And as far as GOP candidates go, Lake tends more toward the extreme, vocally embracing Trump's lies about a stolen 2020 election and calling for the imprisonment of her opponent during the 2022 race.

Lake has since sought to moderate her image, including by telling NBC News in a recent interview that she opposed a federal abortion ban, despite previously endorsing a state-level abortion ban in Arizona that left no exceptions for rape or incest.

That's not to say Gallego has it in the bag — he's more openly progressive than other Democrats who've won statewide office in Arizona in recent years, and polling has shown him roughly even with Lake in a hypothetical matchup.

But while Lake and Gallego duke it out, Sinema can plan for a cushy retirement.

She once told Sen. Mitt Romney, a recently published biography of the Utah Republican said, that she didn't care if her stances cost her reelection.

"I don't care. I can go on any board I want to. I can be a college president. I can do anything," the book quoted Sinema as saying. "I saved the Senate filibuster by myself. I saved the Senate by myself. That's good enough for me."

A spokesperson for Sinema told Business Insider last year that those remarks were "misconstrued and mistaken" during a "game of telephone."