New Jersey state Sen. Samuel Thompson said Monday that he’s leaving the Republican Party and plans to seek reelection this year as a Democrat.

Thompson, 87, said in a phone interview that he decided to leave the GOP after party leaders questioned his fitness for office because of his age.

“The betrayal by so many of my friends — that was too much for me,” he said. “I am not leaving my party. My party leadership has left me.”

Thompson’s departure would expand the Democrats’ edge in the state Senate from 24 to 25 seats in the 40-member chamber.

Messages seeking a response were left with the state and county Republican Party as well as the GOP state Senate office.

Democratic Gov. Phil Murphy said in a statement that he welcomed Thompson to the party and called him a tireless public servant.

Thompson, a former research scientist who served in the Army, said he plans to run for office in this year’s legislative election. He said unlike some lawmakers who work part time as legislators while also holding other jobs, he works only as a legislator.

“It is my life. It gives me something to do every day when I wake up to get there and help people. The alternative is sit at home and just wait to die? I have to be active,” he said. “I think I’m doing a public service.”

Thompson — a supporter of former President Donald Trump — said Trump’s presidency was a success. Asked how he could fit in in the Democratic Party with that view, Thompson paused a moment.

“Everybody is entitled to their own choices and what they’re going to do,” he said.

Thompson represents the 12th Legislative District, which includes parts of Burlington, Middlesex, Monmouth and Ocean counties.

All 120 seats in the Assembly and Senate are up for reelection this year. The primary is set for June, when Thompson said he expected his former party to back a primary challenger against him.

(AP)