Gov. Phil Murphy has been in office for about a month, and on Tuesday a former Republican lawmaker said he's planning to challenge him in 2021.

Former Somerset County Assemblyman Jack Ciattarelli, who left office last year after a failed run in the GOP gubernatorial primary, told The Associated Press that "if asked today, I'm running." Murphy's office didn't immediately respond to a request for comment.

Ciattarelli's decision comes early in Murphy's first term, and just before he unveils his first budget. The governor, who succeeded Republican Chris Christie this year, has promised to raise taxes on millionaires, legalize marijuana and increase school and pension funding.

It's unclear exactly how Murphy would pay for his agenda, because the higher education and retirement spending is estimated to cost more than the new revenue he's proposing.

Ciattarelli said that's one of his principal problems with the liberal-leaning former Goldman Sachs executive who has not held office before.

"He still hasn't come to grips that his promises just aren't realistic," Ciattarelli said.

Ciattarelli is a certified public accountant who owns a medical publishing company. He served in the Assembly from 2012 until this year, leaving office because he was also running for governor last year. He came in second in last year's Republican primary to former Lt. Gov. Kim Guadagno, who lost to Murphy in November.

He said he plans to start a nonprofit to address the state's biggest problems — property taxes, school funding and transportation.

New Jersey is a Democratic-leaning state, with nearly 900,000 more Democratic voters than Republicans.

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