Defense Secretary Mark Esper declined to say Sunday whether he was aware of any political considerations regarding the monthslong hold on almost $400 million in U.S. security aid to Ukraine.

"I'm not going to get into any of that," Esper told "Fox News Sunday." "Again, there is a congressional inquiry underway and I'll leave that process unto itself."

Esper said there were "technical and legal issues" preventing the Pentagon from providing Congress with the requested documents pertaining to the hold on military aid.

The Trump administration placed a hold on the aid as the president and allies were pushing for Ukraine to investigate the Bidens and Democrats. The administration released the aid two days after Congress became aware of a formal whistleblower complaint regarding Trump's actions toward Ukraine.

Those actions are now at the center of the House impeachment inquiry. On Thursday, House Speaker Nancy Pelosi called for her committee chairmen to begin drafting articles of impeachment against Trump.

Esper declined to say why the aid was being withheld in the first place, but said the Pentagon was looking at three things when he was elevated from acting secretary to the Senate-confirmed role.

"One, was the aid necessary and vital to the Ukrainians in terms of defending against Russia?" he said. "No. 2, had the Ukrainians addressed corruption? And that was a congressional concern. And No. 3, were other countries in the region, other allies and partners, assisting them? And, given those three things, we decided to support the provision of Ukrainian aid."

"At the end of the day, the bottom line is most of that aid got out on time and at no time did it have any impact on United States national security," he said.

As the Democratic House Intelligence Committee report notes, roughly $35 million of that congressionally appropriated aid to Ukraine went unspent as the end of the fiscal year — Sept. 30 — neared. Congress passed a bill days before that deadline to ensure that the appropriation would not expire.