How Sinema's retirement changes the Arizona Senate race

Her replacement is unlikely to be a moderate.

March 11, 2024, 3:46 PM

Not with a bang but a whimper.

Overshadowed by the hoopla of the Super Tuesday presidential primaries, Arizona Sen. Kyrsten Sinema revealed last week that she will not seek reelection in 2024. Her decision didn't come as a great surprise, as her reduced fundraising and lack of a signature-gathering campaign to qualify for the November ballot suggested that she wouldn't run again.

Sinema's low-key denouement paled in comparison to the whirlwind that has surrounded her during much of her time on Capitol Hill. Having served three terms in the House as a Democrat, she flipped a battleground Senate seat in 2018, making her a potential star in her party. But once in the Senate, Sinema frustrated many Democrats by opposing changes to the chamber's filibuster rules that might have paved the way for the passage of Democratic-backed legislation dealing with voting rights, abortion rights and President Joe Biden's $3.5 trillion social spending proposal. Because of this, the Arizona Democratic Party voted to censure Sinema in January 2022, and polls suggested Democratic anger toward her could cause her to lose renomination in 2024. Then, after the 2022 midterms, she left the party to become an independent ahead of a potential reelection campaign that short-circuited.

However, Sinema's retirement will have important ramifications for the 2024 election and the future of the Senate. The race to succeed her will now likely pit progressive Democratic Rep. Ruben Gallego against Kari Lake, a Republican close to former President Donald Trump who narrowly lost Arizona's 2022 gubernatorial election. Either prospective successor would mark a notable departure from the more centrist Sinema, thereby shifting the Senate's ideological makeup. And given Sinema's support for the filibuster, her retirement could also lead to fundamental changes in how the Senate functions.

Sinema's retirement and the 2024 Arizona Senate race

Sinema's fundraising lagged in the latter half of 2023, a warning sign that she might not seek reelection. She put together relatively strong numbers in the first half of the year — raising $2.1 million and $1.7 million in the first and second quarters, respectively — but her third quarter total fell to $826,000. This was a conspicuous downtick given her opponents' ample fundraising, but perhaps not surprising given that polls in the first half of the year consistently found Sinema running in a distant third place. Gallego, who announced his Senate bid in January 2023, steadily raised more than $3 million per quarter, while Pinal County Sheriff Mark Lamb, a Republican who announced a run last April, raised $608,000 and $475,000 in the second and third quarters, respectively.

But the stream of retirement chatter surrounding Sinema became a torrent when she reported having raised only $595,000 in the last quarter of 2023. Lake entered the race in October and brought in $2.1 million during the same period, while Gallego once again cleared $3 million (Lamb's fundraising fell to $265,000 as Lake eclipsed him). Overall, Sinema's campaign fundraising in 2023 demonstrated a steady decline that pointed to a potential retirement.

To be clear, Sinema still had a sizable sum of money in the bank at her disposal if she had decided to run. All told, she ended 2023 with $10.6 million, more than Gallego's $6.5 million and Lake's $1.1 million. But her fundraising trajectory also suggested she might struggle to attract enough money to keep up as the general election campaign switched into high gear.

Moreover, Sinema would have also been playing from behind regardless of her finances. Across 17 general election polls in 538's database testing Sinema against Gallego and Lake, Sinema led in none of them and was in third place in all but one. Last fall, a Sinema campaign memo laid out a potential path to victory in which she won at least 60 percent of independents, 25 percent of Republicans and 10 percent of Democrats. But such an approach was built on the figment that voters who identify as independents are actually all independents who would find a centrist, insider-minded senator to be their first choice — a misguided fever that seems highly contagious. Truth is, most independents actually lean toward one party, and only a small share of the electorate is both moderate and independent. Moreover, it would have been difficult to peel off a sizable chunk of Democrats and Republicans if both major parties ran serious, well-funded candidates, as has played out.

Even without Sinema, the Arizona race has all the makings of a toss-up contest, and given the unusual circumstances, it's not totally certain whether Gallego or Lake — who's led Lamb by around 30 points in recent Republican primary polls — might benefit more from her departure. However, early polling suggests Gallego might have the edge here. In surveys since October that compared a prospective Gallego-Lake matchup with or without Sinema in the race, Gallego led Lake by an average of 1 percentage point with Sinema running, but Gallego's edge grew to an average of 3 points over Lake if Sinema wasn't an option.

Digging into available crosstabs from three of these surveys, Gallego tended to gain a bit more support from independent voters than Lake, although not every poll agreed. For instance, an early February poll from Noble Predictive Insights found Gallego's support among independents grew 22 percentage points (from 23 percent to 45 percent) if Sinema wasn't running, while Lake's support among that group only increased by 8 points (from 19 to 27 percent). A mid-February survey from Emerson College/The Hill/Nexstar found a smaller relative shift toward Gallego among independents (+14 points for Gallego, and +11 points for Lake), while an early January survey from Democratic pollster Public Policy Polling conducted for the Replace Sinema PAC actually found Lake doing a hair better among independents with Sinema gone (and beating Gallego among independents in both scenarios).

Still, the overall difference isn't large, so we don't want to overstate the importance of this shift — especially eight months out from the election. There's also reason to wonder if Lake might actually benefit more from Sinema's departure in the long run. In each of those three recent surveys, more Republican than Democratic voters tended to support Sinema or say they were undecided. That suggests that Lake could gain more support over the next few months, should she consolidate support among her party and win the GOP nomination in late July.

At the same time, the 2022 exit poll suggested that Lake lost a few more Republicans than her Democratic opponent, now-Gov. Katie Hobbs, lost Democrats in their gubernatorial matchup. The exit poll also found that Hobbs held a 7-point edge over Lake among independents. Those same shortcomings could afflict Lake in 2024, too, although the electorate will differ in a higher-turnout presidential year.

What Sinema's departure means for the Senate

Regardless of who wins the Arizona race in November, Sinema's successor is likely to be notably more progressive or more conservative than she is. We can get an idea of what this could mean for the Senate's ideological makeup using's DW-NOMINATE metric, which measures the views of members of Congress based on their voting records. Using the metric's first dimension, which measures how liberal or conservative members are, Sinema is the 14th-most conservative member of the Senate Democratic caucus — a group that includes 48 Democrats, Sinema and fellow independent Sens. Angus King of Maine and Bernie Sanders of Vermont. And in the last Congress, her final one as a Democrat, she ranked as the second-most conservative, behind only West Virginia Sen. Joe Manchin.

By contrast, Gallego ranks as more liberal than 62 percent of House Democrats, putting him in the more progressive half of the Democratic caucus in Congress's lower chamber. Were he a senator, Gallego's House voting record would rank him at about the edge of the most liberal third of the Democratic caucus, somewhat akin to Georgia Sens. Jon Ossoff and Raphael Warnock. We don't have a similar score to use for Lake, who is a vocal Trump ally and would score well to Sinema's right. However, we can make a rough guess where Lake might fall based on the voting records of Republican senators who were elected or appointed since Trump won the presidency (so after 2016). On average, those senators sit just inside the most conservative third of the Republican Senate caucus, similar to figures such as Sens. Marsha Blackburn of Tennessee or Ted Budd of North Carolina.

However, the past is not prologue when it comes to a lawmaker's voting record. A classic example of this is Sinema, who had a much more progressive reputation before she came to Washington, but quickly built a moderate record after first winning a House seat in 2012. Gallego had previously been a member of the Congressional Progressive Caucus, the most left-leaning ideological caucus in the House. But he didn't renew his membership this year, saying the dues had risen too much. However, his departure also coincided with his endorsement of a bipartisan Senate deal on border issues that Sinema helped negotiate that failed after Senate Republicans walked away from the table. Meanwhile, Lake, a Trump endorsee who still hasn't accepted her defeat in the 2022 gubernatorial race, has made overtures to "McCain Republicans" in her state with whom she previously clashed — perhaps a sign that she understands she needs those voters to win.

Sinema's departure could also threaten the future of the Senate filibuster, which generally requires a supermajority of 60 votes to advance legislation. Manchin and Sinema ranked as two of the most vocal defenders of the filibuster — and now both are retiring. To be clear, some Democrats who may prefer to keep the filibuster have likely been happy to keep silent and let Manchin and Sinema suck up most of the oxygen on this topic. But along with the retirement of Republican Sen. Mitt Romney of Utah, a broader hollowing out of the Senate's middle will likely remove those most inclined to support the preservation of a longstanding institution like the filibuster, which necessitates bipartisan compromise on most major legislation. Their less-moderate replacements may be more likely to back its destruction — if their party holds a majority and wants to legislate unimpeded.


While Super Tuesday put Sinema's retirement on page two, there was one move she could have made that would have blown up this article's lede: running as No Labels's presidential candidate. The bipartisan, centrist organization is casting about for a notable contender, as some of their potential options have opted against a presidential bid or set their eyes on other offices. However, Sinema said last Thursday that she wouldn't mount a White House bid. Perhaps her failure to muster up enough support in the Senate race was a clear enough indicator of why an independent or third-party candidate can't win that contest, either.

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