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)
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)
Now playing
01:28
Aides resign from office of Dem expected to switch parties
ST. PAUL, MN - NOVEMBER 6:  Former U.S. Vice President Walter Mondale concedes the election to his Republican opponent Norm Coleman November 6, 2002 in St. Paul, Minnesota. Mondale and Coleman were in a race for U.S. Senate that was too close to call the evening before.  (Photo by Mark Erickson/Getty Images)
Mark Erickson/Getty Images
ST. PAUL, MN - NOVEMBER 6: Former U.S. Vice President Walter Mondale concedes the election to his Republican opponent Norm Coleman November 6, 2002 in St. Paul, Minnesota. Mondale and Coleman were in a race for U.S. Senate that was too close to call the evening before. (Photo by Mark Erickson/Getty Images)
Now playing
03:00
Walter Mondale dies at 93
george w bush congress immigration rhetoric cbs intv sot mxp vpx_00000000.png
george w bush congress immigration rhetoric cbs intv sot mxp vpx_00000000.png
Now playing
01:25
Bush calls on Congress to tone down 'harsh rhetoric' on immigration
WASHINGTON, DC - MARCH 23: Sen. Ted Cruz (R-TX) speaks at a Senate Judiciary Committee hearing on "Constitutional and Common Sense Steps to Reduce Gun Violence" on March 23, 2021 in Washington, DC.  Many senators spoke both for and against gun control the day after a shooting in Boulder, Colorado where a gunman opened fire at a grocery store, killing ten people. (Photo by Tasos Katopodis/Getty Images)
Tasos Katopodis/Getty Images
WASHINGTON, DC - MARCH 23: Sen. Ted Cruz (R-TX) speaks at a Senate Judiciary Committee hearing on "Constitutional and Common Sense Steps to Reduce Gun Violence" on March 23, 2021 in Washington, DC. Many senators spoke both for and against gun control the day after a shooting in Boulder, Colorado where a gunman opened fire at a grocery store, killing ten people. (Photo by Tasos Katopodis/Getty Images)
Now playing
03:18
Berman on Cruz's latest tweet: 'The pot calling the kettle violent'
Now playing
01:57
Chuck Hagel criticizes Trump's statement on Afghanistan
gun laws shootings Comer pamela brown nr vpx _00015627.png
CNN
gun laws shootings Comer pamela brown nr vpx _00015627.png
Now playing
02:23
'I can't answer that': Kentucky lawmaker responds to CNN on gun policy
Now playing
02:39
National security adviser: Russia will face consequences if Navalny dies in prison
Rep. Marjorie Taylor Greene (R-GA) speaks during a press conference outside the U.S. Capitol on February 5, 2021 in Washington, DC. The House voted 230 to 199 on Friday evening to remove Rep. Marjorie Taylor Greene (R-GA) from committee assignments over her remarks about QAnon and other conspiracy theories.
Drew Angerer/Getty Images
Rep. Marjorie Taylor Greene (R-GA) speaks during a press conference outside the U.S. Capitol on February 5, 2021 in Washington, DC. The House voted 230 to 199 on Friday evening to remove Rep. Marjorie Taylor Greene (R-GA) from committee assignments over her remarks about QAnon and other conspiracy theories.
Now playing
03:20
Marjorie Taylor Greene lashes out at media after backlash over controversial caucus
AP
Now playing
03:16
Maxine Waters: Jim Jordan is a bully and I shut him down
US Representative Marjorie Taylor Greene, Republican of Georgia, leaves her office on Capitol Hill on February 4, 2021 in Washington, DC.
NICHOLAS KAMM/AFP/Getty Images
US Representative Marjorie Taylor Greene, Republican of Georgia, leaves her office on Capitol Hill on February 4, 2021 in Washington, DC.
Now playing
03:51
Marjorie Taylor Greene launching 'America First' caucus
US President Joe Biden delivers remarks on Russia at the White House in Washington, DC on April 15, 2021. - The United States announced sanctions and the expulsion of 10 Russian diplomats Thursday in retaliation for what Washington says is the Kremlin's US election interference, a massive cyberattack and other hostile activity.
JIM WATSON/AFP/Getty Images
US President Joe Biden delivers remarks on Russia at the White House in Washington, DC on April 15, 2021. - The United States announced sanctions and the expulsion of 10 Russian diplomats Thursday in retaliation for what Washington says is the Kremlin's US election interference, a massive cyberattack and other hostile activity.
Now playing
02:22
White House backtracks on refugees decision after criticism
Biden speaks from the Treaty Room in the White House on April 14, 2021 in Washington, DC.
Andrew Harnik/Pool/Getty Images
Biden speaks from the Treaty Room in the White House on April 14, 2021 in Washington, DC.
Now playing
02:44
'National embarrassment': Biden reacts to mass shootings
MOSCOW, RUSSIA - APRIL 15:  Russian President Vladimir Putin (L) talks to talks to Foreign Minister Sergey Lavrov during a meeting with Uzbekistan President Islam Karimov in the Kremlin on April 15, 2013 in in Moscow, Russia. Karimov is on a state visit to Russia. (Photo by Sasha Mordovets/Getty Images)
Sasha Mordovets/Getty Images
MOSCOW, RUSSIA - APRIL 15: Russian President Vladimir Putin (L) talks to talks to Foreign Minister Sergey Lavrov during a meeting with Uzbekistan President Islam Karimov in the Kremlin on April 15, 2013 in in Moscow, Russia. Karimov is on a state visit to Russia. (Photo by Sasha Mordovets/Getty Images)
Now playing
02:07
Russia to expel 10 US diplomats in 'tit-for-tat response' to Biden sanctions
Now playing
03:10
Avlon: Here's what we know 100 days since the Capitol riot
A Russian flag flies next to the US embassy building in Moscow on October 22, 2018. - US national security advisor John Bolton is in Moscow holding meetings with senior Russian officials following Washington's weekend announcement of withdrawal from the Cold War-era Intermediate-Range Nuclear Forces Treaty, known as the INF. (Photo by Mladen ANTONOV / AFP)        (Photo credit should read MLADEN ANTONOV/AFP via Getty Images)
Mladen Antonov/AFP/Getty Images
A Russian flag flies next to the US embassy building in Moscow on October 22, 2018. - US national security advisor John Bolton is in Moscow holding meetings with senior Russian officials following Washington's weekend announcement of withdrawal from the Cold War-era Intermediate-Range Nuclear Forces Treaty, known as the INF. (Photo by Mladen ANTONOV / AFP) (Photo credit should read MLADEN ANTONOV/AFP via Getty Images)
Now playing
02:17
Political scientist: US-Russia relations are in the toilet
WASHINGTON, DC - JUNE 13: Rep. Michelle Lujan Grisham (D-NM) speaks during a news conference on immigration to condemn the Trump Administration's "zero tolerance" immigration policy, outside the US Capitol on June 13, 2018 in Washington, DC. (Photo by Toya Sarno Jordan/Getty Images)
Toya Sarno Jordan/Getty Images
WASHINGTON, DC - JUNE 13: Rep. Michelle Lujan Grisham (D-NM) speaks during a news conference on immigration to condemn the Trump Administration's "zero tolerance" immigration policy, outside the US Capitol on June 13, 2018 in Washington, DC. (Photo by Toya Sarno Jordan/Getty Images)
Now playing
02:39
Governor settles with former campaign staffer who accused her of sexual mistreatment
(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.