WASHINGTON -- A party-switching congressman drew praise Tuesday from U.S. President Donald Trump and condemnation from Democrats, underscoring how his political fate could hinge on how forcefully he is backed by the president whose impeachment he is refusing to support.

A day before the House was set to cast party-line votes impeaching Trump, New Jersey Rep. Jeff Van Drew stopped short of confirming he will become a Republican but acknowledged he's considering it.

Van Drew told his staff over the weekend that he will become a Republican, a former aide said, prompting at least six top aides to quit in a reaction that underscored the partisan animosity that the impeachment fight has spawned.

"I'm not discussing any of that right now. I'm reevaluating my life and my thoughts," he told reporters in his first public comments about his expected party switch. Later, he added, "This is something I have to work out, but I will announce it and I'll be very clear when I do."

He would not say when he would reveal his decision. Backing Trump as a Democrat on Wednesday would deliver a positive talking point to the GOP, which is expected to unanimously oppose impeachment with support from perhaps one or two Democrats.

House Minority Leader Kevin McCarthy, R-Calif., said in a brief interview that he's had discussions with Van Drew.

"I've told him many times he's more than welcome to join the Republican Party," McCarthy said. Asked if he's offered assistance in getting a committee assignment or hiring staff, McCarthy said, "I'll help him with whatever he needs."

The 66-year-old former state legislator, who's been a political powerhouse in his southern New Jersey district, must figure out how to survive a race in which local Democrats now despise him and Republicans don't want him elbowing them aside.

His race will also test the electoral impact of his party switch on the face of the impeachment showdown, which has sharply divided the two parties. In recent years, congressional party switchers have had mixed records extending their careers.

"I have an election coming up and if they disagree with what I've done, then they will vote me out, and that is something I would very warmly accept as their right," Van Drew said.

Van Drew met last week with Trump, who praised him Tuesday on Twitter.

"Congressman Jeff Van Drew is very popular in our great and very united Republican Party," the president wrote. "It was a tribute to him that he was able to win his heavily Republican district as a Democrat. People like that are not easily replaceable!"

But Rep. Bill Pascrell, D-N.J., called Van Drew's move "a knee-jerk reaction to some poll numbers" that he said showed he'd be unelectable as a Democrat. He said Van Drew had not consulted with his New Jersey colleagues.

"Do you know what we would have done with a guy like that in my neighbourhood in Paterson?" Pascrell told reporters. He later added, "I don't advocate violence."

One rival for the GOP nomination for the seat says he's been told that Trump will endorse Van Drew. Trump has stopped short of doing that so far, and analysts say Trump's backing will be crucial.

"Whatever trouble in the Republican primary Jeff Van Drew might have goes away when Donald Trump throws his arm around the guy," said Ben Dworkin, director of the nonpartisan Rowan Institute for Public Policy & Citizenship in Glassboro, New Jersey.

While Trump's help could be decisive in June's GOP primary for the seat, Van Drew's general election prospects will depend on factors including how liberal the Democratic presidential nominee and the Democrat seeking the House seat are. His district has become increasingly conservative, with Trump carrying it narrowly in 2016 after Barack Obama won it in 2008 and 2012.

"I think Van Drew would be the early favourite, assuming Trump helps him get the nomination," said Patrick Murray, director of the nonpartisan Monmouth University Polling Institute.

David Richter, former CEO of a global construction firm who's seeking the GOP nomination. said local GOP officials have told him Trump will back Van Drew. But he said he thinks he can still defeat him.

"Anybody who runs on the Republican side is against the impeachment. I'm against the impeachment," Richter said. "That's not enough. You also have to be someone who has integrity. You also have to be someone who stood up for Republican principles their whole lives."

Van Drew, a former dentist, was a conservative state senator before he joined Congress, bucking Democrats on issues including gun control and gay marriage.

In his first year in Congress, Van Drew was among a handful of Democrats who voted against Nancy Pelosi becoming speaker. He and Minnesota Rep. Collin Peterson were the only two Democrats who voted in October against starting the impeachment inquiry, and both were expected to oppose impeachment this week, with perhaps a handful of others.

Overall, Van Drew has voted with Trump 7% of the time, according to the data tracking website fivethirtyeight.com. That's one of the higher scores among House Democrats and far beneath the lowest loyalty score for any Republican, which was 35%.

New Jersey Democrats were already bidding him good riddance.

"Congressman Van Drew has long voted against core Democratic values," Democratic Gov. Phil Murphy said in a tweet. "Betraying our party by siding with Donald Trump is the final straw."

Montclair State University political science professor Brigid Harrison, who declared Monday that she would seek the Democratic nomination for Van Drew's seat, called Van Drew "a blind pawn for Donald Trump."

After Republicans captured the House majority in 1994, five Democrats switched to the GOP, including two who lost their next elections. But Rep. Billy Tauzin of Louisiana joined the GOP leadership and became a committee chairman while Georgia Rep. Nathan Deal was elected governor.

"They were more than happy for us to leave," former Rep. Mike Parker of Mississippi said of his former Democratic colleagues in an interview.

In 1999, five House Democrats backed impeaching President Bill Clinton. Three of them eventually switched to the GOP.

Conservative Rep. Justin Amash of Michigan left the GOP and became an independent this year after saying he was open to impeaching Trump. His prospects for reelection next year are unclear.

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Associated Press writers Michael Catalini in Trenton, N.J., Wayne Parry in Surf City, N.J., and Matthew Daly and Kevin Freking in Washington contributed to this report.