Editor’s Note: David Axelrod, a senior CNN political commentator and host of “The Axe Files,” was a senior adviser to President Barack Obama and chief strategist for the 2008 and 2012 Obama presidential campaigns. The opinions expressed in this commentary are his own. View more opinion on CNN.

CNN  — 

Kyrsten Sinema always has had a flair for the dramatic.

Whether through her colorful and flamboyant attire or the keep-them-guessing, idiosyncratic politics that drives many of her Democratic colleagues nuts, the Arizona senator knows how to make a splash.

She did that again Friday, with her announcement that she is leaving the party and registering as an independent – disrupting the warm afterglow Senate Democrats were feeling following Sen. Raphael Warnock’s reelection victory in Georgia.

Democrats were gleeful that Warnock’s victory appeared to give them a 51st vote after two years of a 50-50 split in the US Senate. Sinema’s declaration casts a shadow of uncertainty on the Democrats’ celebratory moment.

But if Sinema’s decision rained on the Democrats’ parade, it seems more a drizzle than a downpour. The practical effect in the next Congress is likely to be slight. She told CNN that she hopes to keep her committee assignments and continue business as usual.

In an interview with Politico, Sinema added, “I don’t anticipate that anything will change relative to the Senate structure.” And there’s good reason to believe her. With the exception of some notable dissents, she has backed President Joe Biden’s positions 93% of the time during his first two years in office.

As it is, Senate Majority Leader Chuck Schumer relies on the votes of two other senators who caucus with Democrats but are technically independents – Bernie Sanders of Vermont, an icon of the progressive left, and Angus King, a moderate from Maine. Sinema now joins their ranks.

It’s unclear whether Sinema will formally caucus with Senate Democrats. But she told Politico that she will not caucus with the Republicans.

So in keeping with her habit of standing out by standing apart, Sinema’s declaration seems meant more as a statement about hyperpartisanship than an institution-shifting change of position.

“Everyday Americans are increasingly left behind by national parties’ rigid partisanship, which has hardened in recent years,” Sinema wrote in an op-ed for The Arizona Republic, explaining her decision to switch political affiliations. “Pressures in both parties pull leaders to the edges, allowing the loudest, most extreme voices to determine their respective parties’ priorities and expecting the rest of us to fall in line.”

An outspoken progressive in her early political life, Sinema has evolved over time to become a leading moderate player in the Senate.

More than most of her colleagues, Sinema has worked easily across party lines in the Senate, helping to forge significant bipartisan legislation on a variety of issues, including infrastructure, gun control and most recently, same-sex marriage.

But laudable as those compromises were, there are few political incentives for bipartisanship in today’s highly polarized party politics, in which the nominating processes are dominated by more ideologically-driven voters.

Sinema’s announcement merely codifies that reality, as she acknowledged in an interview with CNN: “I’ve never fit neatly into any party box. I’ve never really tried. I don’t want to.”

Sinema has enraged many Democrats by using her leverage in a divided Senate to deny some long-sought progressive priorities, including her opposition to higher tax rates on the wealthy. And she has steadfastly opposed ending the filibuster rule that Republicans have used to block key Democratic priorities.

It’s common knowledge in the Capitol that Sinema enjoys warmer relations with some of her Republican colleagues than she does with Schumer.

Back home, Arizona Democrats appeared to have broken up with Sinema even before she broke up with the party. A September poll showed that 57% of Arizona Democrats disapproved of her performance. And Sinema was already facing a likely primary challenge in 2024 from Rep. Ruben Gallego of Arizona, a progressive favorite who represented a significant political threat.

Of course, two years is an eternity in politics. Polls can change. Perhaps Sinema – who declined to address questions about her reelection to CNN – sees a way forward by forging an alliance of disaffected Republicans and Democrats. But such a path would be logistically and politically complicated.

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    Arizona has a history of electing mavericks in the image of the late Republican Sen. John McCain. But Sinema’s bold self-presentation and quirky political style may undercut the value of her independence. In that same September poll, a small majority of independent votes gave her poor ratings.

    In making her announcement, Sinema gave no hint of her future plans. And rather than a re-positioning for future races, it may well be a prelude to a career change for a politician without a partisan home.

    “I see her becoming an independent, but still participating with Democrats – like a married couple who has separated,” a close ally of Sinema’s told me Friday. “I think the final divorce may be when she [decides not to] run.”