More than 15 White House political appointees have been pushed out or have left the Department of Homeland Security since acting Secretary Kevin McAleenan took over in April and have been replaced in some cases with career employees, senior administration officials say.

“McAleenan has systematically removed Trump political staff and replaced it with a group of career employees who have more in common with the Democrat 2020 field than they ever will this administration. This is the quiet resistance that’s been installed at DHS,” a senior official wrote in a text. All officials, none of whom speak for the White House, asked to remain anonymous for fear of retaliation.

In the six months since Trump promoted McAleenan from Customs and Border Protection commissioner to temporarily oversee the 240,000-person department, a total of 17 political appointees in positions close to the acting secretary have departed, and some of them say they did not leave by choice.

A dozen political appointees working in immigration-related public affairs roles at DHS and at its agencies CBP and Immigration and Customs Enforcement have departed. A handful of political appointees working in the secretary’s front office have also left. Those positions included an assistant press secretary, an assistant secretary for public affairs, a speechwriter, and another adviser.

“There has been a mass exodus out of DHS over the last 6 months in every office and agency,” a second official wrote in a message. “There’s no question DHS is a hard place to work, but it became increasingly more difficult once McAleenan and career CBP bureaucrats took over.”

None of the seven public affairs political roles had been filled by the White House. Instead, McAleenan has brought up three employees from CBP, one from the Transportation Security Administration, and one from the Joint Interagency Task Force West. All five are serving on temporary “details,” preventing the White House from filling those jobs.

All of the officials who spoke with the Washington Examiner suggested McAleenan was intentionally installing career employees from CBP and other agencies in top DHS roles meant for the White House to fill with its own selections.

Although the career replacements are referred to as “acting,” officials have worried they are holding down the positions in an effort to block Trump from installing his picks, who are expected to be more conservative than McAleenan on immigration and other issues Trump has focused on since taking office.

Another official described a "toxic" environment at DHS that McAleenan and his trusted career employees are using to push out anyone who disagrees with them rather than accommodate the recommendations of political appointees, who are chosen to represent and carry out a president’s priorities at whichever department they are deployed to.

The same person described working at DHS “like walking on eggshells … just trying to do the best you can, not get stabbed in the back, and keep your job.”

Some appointees left to avoid being affiliated with McAleenan, a longtime Democratic donor whose family has given thousands to 2016 Democratic presidential nominee Hillary Clinton and Barack Obama since 2008. The acting secretary was also named in June by current and former senior administration officials who suspected he purposely leaked to the media an immigration enforcement operation, or raid, to avoid its being carried out because he disagreed with the operation.

“Not many people jump at an opportunity to work for an acting secretary, but not many people they had were willing to risk their own conservative credentials and reputation by working for this acting secretary,” the official wrote in a text.

Neither the White House nor the Department of Homeland Security would comment for this story.