WASHINGTON, DC - NOVEMBER 28:  U.S. Rep.-elect Jeff Van Drew (D-NJ) speaks to members of the media outside a closed House Democrats organizational meeting at Longworth House Office Building November 28, 2018 in Washington, DC. (Photo by Alex Wong/Getty Images)
WASHINGTON, DC - NOVEMBER 28: U.S. Rep.-elect Jeff Van Drew (D-NJ) speaks to members of the media outside a closed House Democrats organizational meeting at Longworth House Office Building November 28, 2018 in Washington, DC. (Photo by Alex Wong/Getty Images)
PHOTO: Alex Wong/Getty Images
Now playing
01:28
Aides resign from office of Dem expected to switch parties
DALLAS, GA - OCTOBER 15: Georgia Republican House candidate Marjorie Taylor Greene endorses Sen. Kelly Loeffler (R-GA) during a press conference on October 15, 2020 in Dallas, Georgia. Greene has been the subject of some controversy recently due to her support for the right-wing conspiracy group QAnon. (Photo by Dustin Chambers/Getty Images)
DALLAS, GA - OCTOBER 15: Georgia Republican House candidate Marjorie Taylor Greene endorses Sen. Kelly Loeffler (R-GA) during a press conference on October 15, 2020 in Dallas, Georgia. Greene has been the subject of some controversy recently due to her support for the right-wing conspiracy group QAnon. (Photo by Dustin Chambers/Getty Images)
PHOTO: Dustin Chambers/Getty Images
Now playing
03:01
GOP congresswoman indicated support for executing Democrats before running for Congress
Bill Currier Oregon GOP Lah vpx
Bill Currier Oregon GOP Lah vpx
PHOTO: Oregon Republican Party
Now playing
02:49
Oregon GOP falsely claims Capitol riot was a 'false flag'
TOPSHOT - US President Joe Biden sits in the Oval Office as he signs a series of orders at the White House in Washington, DC, after being sworn in at the US Capitol on January 20, 2021. - US President Joe Biden signed a raft of executive orders to launch his administration, including a decision to rejoin the Paris climate accord. The orders were aimed at reversing decisions by his predecessor, reversing the process of leaving the World Health Organization, ending the ban on entries from mostly Muslim-majority countries, bolstering environmental protections and strengthening the fight against Covid-19. (Photo by Jim WATSON / AFP) (Photo by JIM WATSON/AFP via Getty Images)
TOPSHOT - US President Joe Biden sits in the Oval Office as he signs a series of orders at the White House in Washington, DC, after being sworn in at the US Capitol on January 20, 2021. - US President Joe Biden signed a raft of executive orders to launch his administration, including a decision to rejoin the Paris climate accord. The orders were aimed at reversing decisions by his predecessor, reversing the process of leaving the World Health Organization, ending the ban on entries from mostly Muslim-majority countries, bolstering environmental protections and strengthening the fight against Covid-19. (Photo by Jim WATSON / AFP) (Photo by JIM WATSON/AFP via Getty Images)
PHOTO: JIM WATSON/AFP/AFP/Getty Images
Now playing
03:40
Weir: Biden promised to help avoid fossil-fuel suicide
US Senate Minority Leader Mitch McConnell (L), R-KY, speaks with US Senator John Barrasso (R), R-WY, after the Republican Policy Luncheon on Capitol Hill in Washington, DC, on January 26, 2021. (Photo by JIM WATSON / AFP) (Photo by JIM WATSON/AFP via Getty Images)
US Senate Minority Leader Mitch McConnell (L), R-KY, speaks with US Senator John Barrasso (R), R-WY, after the Republican Policy Luncheon on Capitol Hill in Washington, DC, on January 26, 2021. (Photo by JIM WATSON / AFP) (Photo by JIM WATSON/AFP via Getty Images)
PHOTO: JIM WATSON/AFP/AFP via Getty Images
Now playing
03:12
CNN breaks down McConnell's telling vote on impeachment trial
duckworth paul
duckworth paul
PHOTO: CNN
Now playing
01:19
Tammy Duckworth to Rand Paul: Stop covering for Trump
PHOTO: senate tv
Now playing
03:53
Watch senators sworn in for Trump's second impeachment trial
Now playing
04:32
'Haven't ruled anybody out': Dominion lawyer on possible lawsuits
WASHINGTON, DC - JANUARY 06: President Donald Trump arrives at the "Stop The Steal" Rally on January 06, 2021 in Washington, DC. Trump supporters gathered in the nation
WASHINGTON, DC - JANUARY 06: President Donald Trump arrives at the "Stop The Steal" Rally on January 06, 2021 in Washington, DC. Trump supporters gathered in the nation's capital today to protest the ratification of President-elect Joe Biden's Electoral College victory over President Trump in the 2020 election. (Photo by Tasos Katopodis/Getty Images)
PHOTO: Tasos Katopodis/Getty Images North America/Getty Images
Now playing
03:00
Haberman reveals list of Republicans Trump wants to 'punish'
Now playing
03:02
Avlon: Republicans offended by Biden's call for unity
PHOTO: Getty Image/CNN
Now playing
02:10
'Really?': Lemon reacts to Haley's take on Trump's trial
WASHINGTON, DC - NOVEMBER 19: Rudy Giuliani holds up a mail-in ballot as he speaks to the press about various lawsuits related to the 2020 election,  inside the Republican National Committee headquarters on November 19, 2020 in Washington, DC. President Donald Trump, who has not been seen publicly in several days, continues to push baseless claims about election fraud and dispute the results of the 2020 United States presidential election. (Photo by Drew Angerer/Getty Images)
WASHINGTON, DC - NOVEMBER 19: Rudy Giuliani holds up a mail-in ballot as he speaks to the press about various lawsuits related to the 2020 election, inside the Republican National Committee headquarters on November 19, 2020 in Washington, DC. President Donald Trump, who has not been seen publicly in several days, continues to push baseless claims about election fraud and dispute the results of the 2020 United States presidential election. (Photo by Drew Angerer/Getty Images)
PHOTO: Drew Angerer/Getty Images North America/Getty Images
Now playing
02:30
Dominion contemplates next legal move after Giuliani lawsuit
US President Joe Biden delivers remarks before signing an Executive Order in the South Court Auditorium at the White House on January 25, 2021 in Washington, DC. (Photo by JIM WATSON / AFP) (Photo by JIM WATSON/AFP via Getty Images)
US President Joe Biden delivers remarks before signing an Executive Order in the South Court Auditorium at the White House on January 25, 2021 in Washington, DC. (Photo by JIM WATSON / AFP) (Photo by JIM WATSON/AFP via Getty Images)
PHOTO: Jim Watson/AFP/Getty Images
Now playing
02:50
Biden thinks US can get to 1.5 million vaccine doses daily
TAMPA, FL - AUGUST 29:  U.S. Sen. Rob Portman (R-OH) waves during the third day of the Republican National Convention at the Tampa Bay Times Forum on August 29, 2012 in Tampa, Florida. Former Massachusetts Gov. Former Massachusetts Gov. Mitt Romney was nominated as the Republican presidential candidate during the RNC, which is scheduled to conclude August 30.  (Photo by Mark Wilson/Getty Images)
TAMPA, FL - AUGUST 29: U.S. Sen. Rob Portman (R-OH) waves during the third day of the Republican National Convention at the Tampa Bay Times Forum on August 29, 2012 in Tampa, Florida. Former Massachusetts Gov. Former Massachusetts Gov. Mitt Romney was nominated as the Republican presidential candidate during the RNC, which is scheduled to conclude August 30. (Photo by Mark Wilson/Getty Images)
PHOTO: Mark Wilson/Getty Images
Now playing
02:16
GOP senator explains why he won't seek reelection
diegal
diegal
PHOTO: CNN
Now playing
02:58
Former Republican: We've got a bankrupt party
(CNN) —  

Much of the staff serving a freshman Democratic congressman resigned on Sunday after sources said the lawmaker prepares to switch to the Republican Party, according to a signed letter obtained by CNN.

Five aides to New Jersey Rep. Jeff Van Drew – Javier Gamboa, Edward Kaczmarski, Justin M. O’Leary, Mackenzie Lucas and Caroline Wood – wrote in the letter that they can “no longer in good conscience continue our service in the Congressman’s employ.”

A sixth staffer also resigned Sunday evening, a source with knowledge of the matter told CNN.

Among the staffers who quit were Van Drew’s legislative director, communications director and his scheduler.

“We greatly appreciate the opportunities that the Congressman has given us, and we are proud of the work we’ve done together on behalf of the people of New Jersey’s Second Congressional District,” the letter said. “Sadly, Congressman Van Drew’s decision to join the ranks of the Republican Party led by (President) Donald Trump does not align with the values we brought to this job when we joined his office.”

The resignations come as Van Drew, who strongly opposes House Democrats’ impeachment of Trump, has told colleagues of his intentions to switch parties, according to two sources.

Internal polling has shown he was losing major support from Democrats in the district, Democratic sources told CNN on Saturday. Switching parties would allow Van Drew to avoid a Democratic primary challenge for his seat.

Van Drew was one of just two Democrats who in October voted against formalizing the impeachment inquiry, and announced earlier this month that he would vote against all articles of impeachment on the House floor. The full House of Representatives is expected to vote this week on two House Judiciary Committee-approved articles of impeachment, which will set up a trial in the Senate.

After voting against the formal inquiry in October, the New Jersey congressman said in a statement that “without bipartisan support I believe this inquiry will further divide the country tearing it apart at the seams and will ultimately fail in the Senate.”

News of Van Drew’s intention to switch parties drew swift condemnation from Democrats.

New Jersey Gov. Phil Murphy on Saturday assailed Van Drew, who represents a district where the Republican President is popular, as “willing to enable” Trump “just to try to salvage his own election.”

“Betraying our values by siding with Donald Trump is the final straw and made it impossible for him to continue being supported by our party, as grassroots activists, local party leaders in his district, and I have made clear in recent weeks,” Murphy, a Democrat, said in a statement. “This party switch is cynical and desperate, and I am confident that a Democrat who shares the values and priorities of our Democratic Party will hold this seat.”

Democratic Rep. Steve Cohen of Tennessee told CNN’s Ana Cabrera on “Newsroom” that Van Drew is “making a serious mistake.”

“I understand that he feels if he votes against impeachment, he’ll lose in a Democratic primary and he could,” Cohen said Sunday. “But you know he got elected with Democratic votes under a Democratic banner which he ran under for 30 years or so. I think he was a Senator and a Mayor and a Representative and all, and he got Democratic money including Democratic Congressional Campaign Committee money, and to turn and go to be a Republican, it’s kind of strange.”

He added: “I’ve heard of rats jumping off a sinking ship, but very few of them jump onto a sinking ship.”

Van Drew’s district – a district that had voted for Barack Obama in 2008 and 2012, before voting for Trump in 2016 – had been held by former Republican Rep. Frank LoBiondo for 24 years before Van Drew won the seat in 2018. In that race, Van Drew ran against a Republican candidate, who after making controversial remarks against diversity, lost the support of the National Republican Congressional Committee.

On Saturday, House Minority Leader Kevin McCarthy, a California Republican, welcomed Van Drew to the Republican Party.

“I want to tell Jeff Van Drew that he is welcome in the Republican Party, not just by me but by our conference, and we would support him and we would welcome him to join,” McCarthy told Fox News’ Jeanine Pirro.

UPDATE: This story and headline have been updated to reflect that a sixth staffer resigned Sunday.

CNN’s Veronica Stracqualursi and Lauren Fox contributed to this report.