WASHINGTON — New Jersey Rep. Jeff Van Drew is leaving the Democratic Party to become a Republican, President Donald Trump announced Thursday, confirming during a White House meeting with his new GOP ally a party switch that had been expected since last weekend.

Trump introduced Van Drew in an Oval Office meeting that also included Vice President Mike Pence and House Minority Leader Kevin McCarthy (R., Calif.).

“Jeff will be joining the Republican Party," Trump said. “It’s a very exciting announcement.”

Van Drew said he has always been a moderate, and blasted unnamed Democrats for moving the party too far left.

“I believe that this is just a better fit for me," he said. “This is who I am.”

Van Drew rattled off a string of issues he said pushed the party away from him, criticizing the Green New Deal proposal and accusing some Democrats of downplaying America’s exceptionalism. He praised Trump’s record on the economy and pledged loyalty to his new party.

“You have my undying support, always," Van Drew said. Trump responded, saying: “I’m endorsing him.”

The announcement ended days of political uncertainty for Van Drew, after the revelation last Saturday that he planned to switch parties. He joins a rare group of defectors in recent years. Former Alabama Rep. Parker Griffith, a longtime Democrat, became a Republican in 2009, only to lose in a GOP primary next year. That same election cycle, Pennsylvania Republican Sen. Arlen Specter bolted to the Democrats before losing the 2010 primary to Joe Sestak.

Pence added Thursday that “another public official from New Jersey” will be following the South Jersey congressman’s lead. He did not give any details.

Van Drew’s vocal opposition to impeachment enraged Democratic leaders and activists, and prompted plans for him to switch parties.

He voted against both articles of impeachment late Wednesday, disagreeing with the vast majority of his Democratic colleagues, who maintained that Trump abused his power and obstructed Congress.

During the daylong impeachment debate Wednesday Van Drew sat with Republicans on the House floor, shaking hands with GOP lawmakers and congratulating their leaders after their strident defenses of Trump.

On Dec. 11, Van Drew learned from an internal poll just how much his stance on impeachment imperiled his chances to win a Democratic primary. He proceeded to cut off contact with key allies, and two days later was at the White House to discuss plans to become a Republican.

Van Drew said his decision to switch parties began when a Democratic county chairman, whom he didn’t name, told him he would not get party support if he opposed impeachment.

Van Drew received a letter weeks ago from Atlantic County Democratic Chairman Michael Suleiman indicating concern at the South Jersey congressman’s stance on impeachment.

“I am imploring you to vote in favor of impeachment,” Suleiman said. “A ‘no’ vote on impeachment will suppress Democratic turnout down-ballot, which my organization cannot sustain."

Van Drew may have hoped defecting to the GOP would ease his path to reelection in a conservative-leaning district. But local Republicans have hardly been welcoming, questioning Van Drew’s mostly liberal voting record and relationship with the state’s Democratic machine as troubling.

“He will have to prove he is with us on more than just the issue of impeachment,” Jacci Vigilante, chair of the Gloucester County GOP, said recently.

All three Republican candidates who were running for his seat will stay in the race, for the moment undeterred by Trump’s Oval Office endorsement of Van Drew.

“Bring it on,” said Bob Patterson, a Republican candidate for Van Drew’s seat, in a statement. "South Jersey citizens deserves a congressman who will fight for them and their conservative values — not a liberal opportunist who fights for himself.”

Trump has fired off a couple of tweets lauding Van Drew, but it remains to be seen how hard he will campaign for the longtime Democrat in a Republican primary.

At least eight members of Van Drew’s House staff have resigned, along with all three members of his campaign staff. Six of his former aides will be hired by New Jersey Democratic Rep. Frank Pallone to work on the House Committee on Energy and Commerce, which Pallone chairs, according to sources familiar with the matter.

“Congressman Van Drew is joining a Republican Party led by President Trump that kowtows to special interests, gives the wealthy big tax breaks, and denies climate change,” Pallone, a Shore area Democrat, said in a statement. “It’s unfortunate he has chosen to climb a career ladder that’s doomed to collapse.... In 2020, we will be working hard to elect a Democrat in NJ-2.”

Meanwhile, Montclair State University professor Brigid Callahan Harrison has already announced she will run in the Democratic primary. Harrison, a longtime resident of the district, has already won support from State Senate President Stephen Sweeney and six local Democratic Party chairs.

Atlantic County Freeholder Ashley Bennett, a Democrat, plans to announce her candidacy Friday, and Amy Kennedy, a former public-school teacher and wife of former Rep. Patrick Kennedy (D., R.I.), has announced an exploratory committee for the seat.

On Tuesday, all the county Democratic chairs in his congressional district demanded Van Drew that return campaign cash that was given to him as a Democrat. “It’s time for Van Drew to man up and do the right thing for once,” they said in a joint statement, "and return every dime he received since he sold us out.”