As of Saturday afternoon, it was still unclear if Van Drew would make the announcement before the House votes on impeachment, which is expected Wednesday.

“It was supposed to be bipartisan, it was supposed to be incontrovertible. It was supposed to be something that was always on the rarest of circumstances,” Van Drew told reporters about impeachment earlier this week. “Well it’s not bipartisan.”

Republicans were excitedly touting the news on Saturday, describing it as a huge blow to Democrats' effort to impeach the president, which Trump and other GOP leaders have repeatedly decried as a "partisan witch hunt." The move is also certain to score major points with Trump, whose support could be crucial in a crowded GOP primary. Trump and Van Drew are expected to hold an event together next week, according to sources on Capitol Hill.

But Democrats were already brushing off the party switch, saying Van Drew was making the calculation purely based on politics and voters would see right through his self-interested motivations in November 2020.

And Democrats are quick to note that Van Drew's departure is unlikely to impact the impeachment vote tally in any way. Democratic leadership had already been expecting a handful of their members to vote against impeachment, including Van Drew, next week.

Multiple senior Democrats tried to reach out to the New Jersey freshman on Saturday but were unsuccessful. Van Drew did not respond to calls and texts from POLITICO seeking comment.

Rumors had swirled around Capitol Hill this week that Van Drew was considering leaving the Democratic Party but he strongly denied those claims on multiple occasions. Van Drew flipped his GOP district in southern New Jersey, helping deliver Democrats the House majority. The district, which still leans Republican, voted for Trump in 2016.

The stunning move comes amid new polling commissioned by Van Drew's campaign that shows his approval ratings are under water with Democratic voters in his district. Just 24 percent of Democratic primary voters said Van Drew deserves to be reelected to Congress, and only 28 percent said he deserves to be the Democratic nominee in next year’s election.

TargetSmart conducted the survey from Dec. 7-10 of 390 likely Democratic primary voters, according to a source familiar with the polling. It also found 71 percent of voters would be less likely to support Van Drew in his reelection if he voted against impeachment. Only 22 percent said they would be more likely to support him.

If Van Drew voted to impeach Trump, 69 percent would be more likely to back him in next year's election and 22 percent would be less likely.

One Republican familiar with the situation said Saturday afternoon that the crossover was imminent. “In the works as we speak,” the member said, noting that Van Drew had a meeting “at length” with Trump on Friday. The meeting between Trump and Van Drew was first reported by the Washington Post.

Republicans on Capitol Hill had been whispering all week about whether Van Drew might join their ranks — some senior Republicans had even encouraged the move.

Van Drew does not currently have any primary challengers — but Brigid Harrison, a professor at Montclair State University, had been publicly mulling a run, citing Van Drew's opposition to impeachment.

He already has three GOP challengers, including businessman David Richter, who has the ability to self-fund and has already loaned his campaign $300,000.

Van Drew, a dentist and former state senator whose district includes the southern portion of the state, was a long sought-after Democratic recruit. He rebuffed entreaties to run until Republican Rep. Frank LoBiondo decided to retire last cycle.

Trump carried the district by 5 points in 2016. Van Drew won it by 8 points in 2018, beating Seth Grossman, an opponent whom national Republicans disavowed after discovering he had made racially insensitive comments.

Local Democrats were enraged by the news. Atlantic County Democratic Chairman Michael Suleiman, whose county is entirely within the 2nd Congressional District, called Van Drew a “coward” who “took the easy way out.”

“It’s one thing to vote against impeachment, but instead of owning up to his constituents and explaining to them why he’s doing what he’s doing, he’s now decided to just completely abandon the Democratic Party and switch,” Suleiman said. “It’s just unconscionable.”

Sarah Ferris, Matt Friedman and Andrew Desiderio contributed to this report.

