A state legislator has changed her party registration to Republican from Democrat in the Tar Heel State, giving the GOP a supermajority that will allow it to essentially govern the state without input from Governor Cooper, a Democrat. 

Representative Tricia Cotham announced her decision on Tuesday at a press conference at the North Carolina Republican Party headquarters. “This modern day Democratic Party has become unrecognizable to me,” she said, flanked by the house speaker, Tim Moore, and Congressman Dan Bishop.

“The party wants to villainize anyone who has free thought,” Ms. Cotham added. She said that her Democratic colleagues have been privately criticizing her for her more moderate beliefs since the beginning of the legislative session in January. 

Her departure from the Democratic Party immediately creates a new balance of power at Raleigh. The Republican Party already holds a supermajority of seats in the state senate, allowing it to override the governor’s veto, but last year it fell short by just one seat to win a supermajority in the lower chamber. 

Republicans have held both houses of the North Carolina legislature for more than a decade, but this is the first time they will have the power to pass bills without any input from the Democratic governor. In March, Mr. Cooper vetoed a bill that relaxed gun permit restrictions and background checks, only to have the legislature override him. Ms. Cotham’s absence from that vote led many of her Democratic colleagues to criticize her privately, she claimed.

The gun bill override could be just the opening salvo to a new future of North Carolina politics in which a governor is essentially rendered powerless. On issues like abortion, legislative redistricting, and school choice, Mr. Cooper could be cut out of the conversation entirely should Republicans maintain complete party unity. 

The house minority leader, Representative Robert Reives, said Ms. Cotham pulled a bait-and-switch on her voters by campaigning on key Democratic causes last year. “Tricia Cotham campaigned as a Democrat and supporter of abortion rights, health care, public education, gun safety, and civil rights,” Mr. Reives said in a statement. “The appropriate action is for her to resign so that her constituents are fairly represented.”

The governor called Ms. Cotham’s party switch “disappointing,” but held out hope that she would remain a fairly reliable vote on issues like “women’s reproductive freedom, LGBTQ rights, and strong public schools.” 

Ms. Cotham won her first election last year to represent the affluent, heavily Democratic suburbs of Charlotte. She was elected with nearly 60 percent of the vote.  

Mr. Moore introduced Ms. Cotham at the press conference on Tuesday, saying his caucus has a more diverse range of viewpoints than those on the other side of the aisle. “We understand that having a big tent with ideas across the spectrum is not just what makes a party healthy, but governing effective,” Mr. Moore said. 

He added that he has previously spoken to “other Democrats” about the party’s movement to the left, hinting at other possible defections.