Several alarmed White House career budget staffers alerted House appropriators when the Office of Management and Budget last summer placed a political appointee in charge of a hold on $400 million in foreign assistance to Ukraine.

Those OMB civil servants questioned a move to put Trump administration political hire Michael Duffey, associate director of national security programs, in control of the freeze, a Democratic aide told POLITICO. But White House budget officials contend there was nothing unusual or improper about shifting the responsibility into the hands of Duffey, and that the decision had nothing to do with the career staff concerns that the hold was not legal.

The administration’s halt on foreign assistance to Ukraine this summer is now at the center of the impeachment investigation led by House Democrats into whether President Donald Trump pressured Ukraine’s president to investigate his political rival, former Vice President Joe Biden, while using the aid as leverage.

At least five House committees are investigating the administration’s decision to halt the funds. Earlier this week, House Democrats issued subpoenas for documents from the Pentagon and OMB, hoping to unearth more details about the directive.

OMB’s decision to delegate authority to Duffey, former executive director of the Republican Party of Wisconsin, despite career staff's objections proved so concerning that House Appropriations Chairwoman Nita Lowey (D-N.Y.) and House Budget Chairman John Yarmuth (D-Ky.) broached the subject in a Sept. 27 letter to the agency.

In their letter, the Democrats questioned the agency’s “unusual and seemingly unprecedented step” to delegate authority to a political appointee, “in lieu of career civil servants who have historically been the designated officials responsible for overseeing and executing these technical budget documents.”

But it’s not unusual for political appointees to be involved in the process, according to a senior administration official, who contended that Duffey’s involvement wasn’t triggered by legal concerns raised by career staff. The acting head of OMB can delegate authority to anyone within the agency on such issues, the official said.

The Wall Street Journal first reported that Duffey was charged with holding up the Ukraine assistance after career staff questioned the legality of delaying the funds.

POLITICO first reported on Aug. 28 that the Trump administration had frozen the money, which is meant to combat Russian aggression in the region. The aid has provided a critical lifeline to Ukraine, helping to build out a ragtag army into a better-armed and professional force. OMB lifted the hold on Sept. 11.

The House Appropriations Committee first found out about the freeze on Aug. 14. Staff then pressed OMB and the Pentagon for answers for two weeks, receiving little information. Only after POLITICO’s story published on Aug. 28 did House appropriators receive a statement from OMB about the freeze on foreign assistance, according to a Democratic aide.

OMB has contended that the administration only wanted to review the funds to ensure the money is being used in the best interest of the United States, while Trump has complained that other countries aren’t paying their fair share.

But text messages recently provided to Congress by former U.S. representative to Ukraine Kurt Volker included discussion of whether military aid was being withheld from Ukraine to force President Volodymyr Zelensky into investigating Biden and his son, Hunter.

Duffey also helped orchestrate the Trump administration’s push earlier this year to effectively force the cancellation of billions of dollars in State Department and USAID funds through a presidential rescission package, although the administration dropped that effort.

Kyle Cheney, Andrew Desiderio, Bryan Bender and Wesley Morgan contributed to this report.