TRENTON, N.J. — The second-in-command to Republican Gov. Chris Christie, who mostly stood by his side for seven years before publicly breaking with him last year over his support of Donald Trump and an increase in the state’s gas tax, entered the race to replace him Thursday.

Lt. Gov. Kim Guadagno filed the documents with the Election Law Enforcement Commission to run in the Republican primary, ELEC spokesman Scott Miccio said. Guadagno is the state’s first lieutenant governor, elected with Christie in 2009 and re-elected in 2013.

Guadagno is an attorney who served as a federal prosecutor in New York and later moved to New Jersey, where she served as Monmouth County sheriff.

She enters the race having served as an ally of the governor, who is deeply unpopular in New Jersey at the moment. But they have had their disagreements, and the federal trial in the George Washington Bridge scandal last year cast light on more stressful points in their relationship.

David Wildstein, who pleaded guilty to being the architect of the political revenge plot, testified that he was told that Guadagno had been “frozen out” by the governor.

Bridget Kelly, the governor’s former deputy chief of staff who was convicted, testified that the relationship between Christie and Guadagno was “stressful.”

“There were times where she was kind of put in a box (by Christie) and wasn’t permitted to do a whole lot,” Kelly said. “She wasn’t allowed to see his schedule.”

In the run-up to her entering the contest, she made headlines by splitting from the governor. She was critical of Trump and split with the administration on a proposed constitutional amendment to dedicate gas tax proceeds to transportation. She argued that the amendment would be a back door to more borrowing, but voters disagreed with her and approved it.

Christie notably bumped Guadagno as the keynote speaker last year at an annual conference of local governments in Atlantic City. The speech came after Guadagno had criticized transportation measures the governor brokered, including the gas tax hike and the constitutional amendment.

Among her top duties over the last seven years has been working with businesses to stay in New Jersey, including heading up a commission aimed at cutting regulations. She’s well-known in the state’s business community for her accessibility, regularly handing out her cellphone number.

She also served as acting governor while Christie increasingly traveled out of state, first as chairman of the Republican Governors Association in 2014, then as a presidential candidate in 2015.

She joins Republican Assemblyman Jack Ciattarelli, among others, competing in the June 6 primary. Ciattarelli announced Thursday that he is undergoing treatment for cancer in his neck and is scaling back his campaign. He said that he plans to resume campaigning full time in February and that there is a good chance he will beat the cancer.

Democrats running include former Goldman Sachs executive Phil Murphy, Assemblyman John Wisniewski, state Sen. Ray Lesniak and former Clinton administration treasury official Jim Johnson.