"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.

Though she was initially elected as a Democrat, Sinema left the Democratic Party at the end of 2022 and has been a consistent thorn in the side of Democratic majority in the Senate since President Joe Biden took office. She and Sen. Joe Manchin (D-West Virginia) — who is also retiring at the end of the year — were the two deciding votes that killed Biden's signature "Build Back Better" legislative package, which would have guaranteed universal pre-K and child care to parents, paid family leave and additional funding for environmental programs, partially funding by an additional tax on the wealthiest Americans.

In March of 2021, Sinema angered Democrats as the deciding vote to kill legislation to raise the federal minimum wage to $15 an hour during the height of the Covid-19 pandemic. After stepping onto the Senate floor, Sinema gave the clerk a thumbs-down, with an additional curtsy, before turning around and leaving the chamber. She also rebuffed Democrats' efforts to get rid of the filibuster, allowing Republicans to maintain a blockade over any legislation that failed to garner the 60 votes needed to advance a bill to the full floor for debate after a cloture motion was invoked.

Later that year, immigration activists from the group Living United for Change in Arizona (LUCHA) confronted Sinema in a public restroom over her refusal to back a pathway to citizenship for so-called "Dreamers," or children of undocumented immigrants who were brought across the border at a young age. LUCHA defended the bathroom confrontation, saying Sinema "denied our requests, ignored our phone calls, and closed her office to her constituents," and that she "hasn’t had a public event or town hall in years."

That confrontation happened at the Phoenix campus of Arizona State University, where Sinema taught a graduate-level course on campaign fundraising. The Intercept's Ken Klippenstein likened Sinema's course to "getting rich people to give you money." He reported that Sinema racked up nearly $1 million in campaign donations from groups opposed to the Build Back Better bill she helped defeat, and that she "has received tens of thousands of dollars in maxed-out contributions from private equity partners and investment firm CEOs who stand to lose in the event of a tax hike on corporations or the rich."

In January, Sinema made headlines after a Daily Beast investigation found that she had spent more than $200,000 in taxpayer money on private jet flights since 2020. Sinema reportedly spent roughly $116,000 in 2023 alone. Almost all of the flights were within Arizona, and were for one or two-day trips. The Beast observed that the cost of Sinema's flights last year were more than the annual salaries of nearly all of her staff.

With Sinema no longer running, the Arizona US Senate race in 2024 will be between Rep. Ruben Gallego (D-Arizona) and former newscaster Kari Lake, the presumptive Republican nominee who ran a failed campaign for governor in 2022.