In a move that undoubtedly further alienated her from the party, Sinema helped defeat President Joe Biden’s renomination of National Labor Relations Board Chairwoman Lauren McFerran, a Democrat.

Sinema’s vote against McFerran dashed hopes from Democrats to Trump-proof the federal agency that oversees U.S. labor law by keeping a Democratic NLRB under the incoming president.

A procedural vote to advance McFerran’s renomination to another five-year term failed 49-50. Sinema and Sen. Joe Manchin (I-WV), who also caucuses with Democrats and is retiring, voted with all Republicans against McFerran.

“It is deeply disappointing, a direct attack on working people, and incredibly troubling that this highly qualified nominee, with a proven track record of protecting worker rights, did not have the votes,” Senate Majority Leader Chuck Schumer (D-NY) said.

Sinema’s extended absence left Democrats wondering her whereabouts and whether she would return in her final weeks as a senator before the current Congress’s legislative business concludes next week. Her office did not respond to requests for comment about the absence that included 16 missed votes on district judges since Dec. 2.

Senate Majority Whip Dick Durbin (D-IL) told the Washington Examiner prior to Sinema’s surprise return Wednesday that he did not have contact with her and was unaware of her location.

“Nope, I sure don’t,” Durbin said, shaking his head. “You know, she’s an independent.”

Prior to the McFerran vote, Sinema’s absence had yet to affect Democrats’ ability to pass votes and confirm presidential nominees. Senate Democrats, which includes Sinema, have a one-vote 51-49 majority.

“We’ve won by one vote, two votes, three votes. It’s a perilous journey, but we’re successful so far,” Durbin said minutes before she opposed McFerran.

Sinema also snubbed the State Society of Arizona’s holiday reception last week in Washington, D.C., which was set to host her as a guest of honor to recognize her time as a senator since 2019, the Arizona Republic reported.

Facing long reelection odds, Sinema decided not to run for reelection in March. Then, the missed votes started to pile up, tarnishing her once steady and reliable attendance.

Since announcing her retirement, Sinema has boasted one of the worst attendance records, skipping roughly one-third of the more than 200 votes held. In the roughly same time period before deciding against reelection, Sinema missed less than 2% of the 288 votes held.

McFerran’s term expires Monday. Her reinstalment would’ve secured a Democratic NLRB majority on the five-person panel tasked with protecting organized union labor until at least August 2026, at which point Trump could have replaced another expiring Democrat with a Republican.  

The NLRB’s current makeup is three Democrats, one Republican, and one absent Republican seat. The agency may not have more than a 3-2 partisan majority for either party. Each seat’s term runs five years, regardless of when members are seated.

Trump will be tasked with replacing McFerran, as well as choosing someone for the open Republican seat, allowing him to swing the NLRB back to a 3-2 GOP majority. Following the failed McFerran vote, Senate Democrats scrapped a procedural vote to advance Biden nominee and labor attorney Joshua Ditelberg to fill the open Republican slot.

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Conservatives opposed McFerran over a range of NLRB decisions made under her leadership that they say have been anti-business, restricted employer free speech, undermined secret ballot union elections, and violated the Civil Rights Act from labor law interpretations.

Sen. Bill Cassidy (R-LA), the top Republican on the Senate committee with jurisdiction over labor issues, accused Democrats of orchestrating a “partisan attempt to deny President Trump the opportunity to choose his own nominees and enact a pro-America, pro-worker agenda with the mandate he has from the American people.”