Actress and activist Cynthia Nixon, star of the long-running cable series “Sex and the City,” is running for governor of New York, challenging two-term Gov. Andrew M. Cuomo from the left in this year’s Democratic primary.

“Something has to change,” Nixon said in her campaign’s launch video Monday. “We want our government to work again, on health care, mass incarceration and fixing our broken subway. We are sick of politicians who care more about power than they do about us.”

Nixon, 51, has never sought office before but has become increasingly involved in liberal politics, especially on issues such as public school funding. She was an early endorser and surrogate for New York City Mayor Bill de Blasio and has spoken at fundraisers for Planned Parenthood, speaking out on the group’s behalf when Republicans have attempted to cut off its federal funding. If elected, she would be the first female governor of New York and the first elected elected openly gay governor of any state.

Cuomo, who is seeking a third term, has mocked the idea of a Nixon challenge since it was rumored last month. Asked by reporters this month why she might run against him, Cuomo joked that she was put up to it by his enemies.

“It was either the mayor of New York or Vladimir Putin,” Cuomo said on a conference call. “Normally name recognition is relevant when it has some connection to the endeavor. If it’s just about name recognition, then I’m hoping Brad Pitt, Angelina Jolie and Billy Joel don’t get into the race.”

In the latest Siena Poll, the first that tested Cuomo against Nixon, the governor enjoyed a 47-point lead and leads of 28 and 29 points over the leading Republican candidates. But 48 percent of voters told the pollster that they would vote to reelect Cuomo, and 46 percent said they would prefer to elect someone else.

Zephyr Teachout, an author and law professor who challenged Cuomo in the 2014 primary and is now serving as treasurer for Nixon’s campaign, argued that Cuomo is more vulnerable to a challenge from his left. Democrats, she said, have grown increasingly frustrated by the Independent Democratic Caucus, a group of senators who have kept the Republican Party in charge of the New York state Senate.

“One of the effects of Trump’s election is people being much more aware of Cuomo’s work to keep Republicans in control of the Senate, and we have corruption scandals, year after year, that come back to the governor,” said Teachout, who ran unsuccessfully for Congress in 2016.

Cuomo, who won a lower-than-expected 62 percent of the vote when Teachout challenged him, had been making moves to shore up his left. He had brought Sen. Bernie Sanders (I-Vt.) to the state to talk up a free college tuition plan, promoted tougher gun safety legislation, and picked high-profile fights with President Trump. But Teachout, who had been talking to Nixon about a run for months, said that any Cuomo attempts to portray her as less than serious would fall flat.

“She rides the subway every day,” Teachout said. “She grew up with a single mom. She’s really smart — she asks a lot of questions, and she sees the way all of these issues are tied together by the way money in politics works in New York.”