“We understand that her decision to register as an independent in Arizona does not change the new Democratic majority control of the Senate, and we have every reason to expect that we will continue to work successfully with her,” Jean-Pierre stated in a statement.

Others in the administration believe that her shift will not change their interactions with her in any way. the It could take months to complete. One person was involved in shaping the White House approach to She spoke under anonymity to describe her as difficult and contrarian but she eventually had supported her. the President on critical votes, giving Mr. Biden (and Democrats) a successful legislative record to promote.

Arizona was quick to react to her decision and created a group. to They had already started a primary campaign against her and said that they would now be focusing on her removal in the general election.

“Today, Kyrsten Sinema told us what we’ve already known for years: She’s not a Democrat, and she’s simply out for herself,” the Primary Sinema campaign stated in a statement. “In one way, Sinema just made our jobs easier by bowing out of a Democratic primary she knew she couldn’t win. Now, we’ll beat her in the general election with a real Democrat.”

Representative Ruben Gallego, a Democratic Arizona House member and potential candidate for the Ms. Sinema’s seat, issued a statement saying, “Unfortunately, Senator Sinema is once again putting her own interests ahead of getting things done for Arizonans.”

It was clear that the Move was in Ms. Sinema’s political interest. A recent poll by Civiqs highlighted her unpopularity with Democrats in Arizona — just 7 percent approved of her — while 27 percent of Republicans and 29 percent of independents in the The state held a favorable opinion. However, the majority of Republicans and half the independents disapprove of her.

Party In some cases, switching is common. the Senate when lawmakers see political advantages in such a move. After losing in a Democratic Primary in 2006, Senator Joseph I. Lieberman from Connecticut ran as an independent and won. to caucus of majority Democrats Senator Arlen Speter of Pennsylvania left the Republican Party In 2009, Democrats joined with Democrats in supporting some initiatives. the Obama administration, but it was defeated in a Democratic primary.