When the Trump administration first decided to sell Javelin anti-tank missiles to Ukraine, officials at the Office of Management and Budget (OMB) moved to temporarily pause the effort, according to multiple sources briefed on the matter.

The unusual move didn’t just foreshadow the huge fight that has President Donald Trump now facing impeachment. It also caught the eye of congressional investigators in the impeachment inquiry. This summer, OMB delayed the provision of a second shipment of military aid to Ukraine. An Intelligence Community whistleblower pointed to the Trump administration’s decision to temporarily hold up the aid as a source of concern about alleged efforts to extort Ukraine. Democrats responded by opening an impeachment inquiry.

In 2017, with the enthusiastic support of Defense Sec. Jim Mattis and Secretary of State Rex Tillerson, the Trump administration moved to greenlight sending of over $40 million worth of Javelin anti-tank missiles to Kyiv. But enthusiasm for the move wasn’t unanimous; in late 2017, as the interagency process moved forward, OMB temporarily gummed it up.

OMB’s move frustrated some officials in President Donald Trump’s administration, who saw delivery of the lethal aid as a key national security priority. It let them support Kyiv in a way that the prior administration hadn’t; despite pressure from Congress, the Obama administration declined to send lethal aid to Ukraine, arguing it would inflame tensions in the eastern part of the country. Russian-backed separatists started fighting against Kyiv there in 2014, when militias—which included Russian troops—annexed the Ukrainian-held territory of Crimea, along with other areas in the eastern part of the country.

In the first year of the Trump administration, Mulvaney was OMB director. His agency was seen as an outlier in its hesitance regarding the Javelins.

“ Why was Mick Mulvaney upholding Susan Rice and Barack Obama’s bad Ukraine policy? ” — Trump administration official

“Why was Mick Mulvaney upholding Susan Rice and Barack Obama’s bad Ukraine policy?” one administration official told The Daily Beast.

The White House did not respond to a request for comment.

The OMB postponement didn’t last long, according to another source briefed on the matter. But the office’s ability to slow down the process is itself “unusual,” per a U.S. government official who works on arms sales.

“It is not their brief to have an opinion on the national security or foreign policy implications of arms sales,” the official said.

The incident has been discussed during Congress’ closed-door impeachment inquiry. Investigators are deeply interested in the history of the Trump administration’s Ukraine policy.

“If I were an enterprising reporter, I’d spend a little bit of time on the issue of Javelin missiles,” Rep. Gerry Connolly (D-VA) told reporters after stepping out of a closed-door deposition on Wednesday.

Mulvaney’s skepticism about the Javelin sales has drawn the attention of impeachment investigators, who are scrutinizing his work on Ukraine policy. He is already a central focus of the impeachment inquiry, thanks to his role in delaying nearly $400 million of U.S. security aid to Ukraine. Officials have testified that the Trump administration temporarily withheld that aid in an effort to force Kyiv to announce an investigation of the Bidens.

Various officials, including the anonymous whistleblower whose account launched the impeachment probe, have said that OMB—which remains under Mulvaney’s leadership after his promotion to Trump’s acting chief of staff—declined to explain to the Department of State, the Pentagon, and Capitol Hill why it froze the 2019 aid package. The postponement generated quiet confusion and frustration for months. It is highly unusual for OMB to get involved with funds that had already been apportioned by Congress, as the Ukraine aid had.

During a press briefing on Oct. 17, Mulvaney himself admitted to using the support money to pressure Ukraine to open an investigation into the company Hunter Biden was linked to and theories that Kyiv meddled in the 2016 election. Those things, said Mulvaney, were “why we held up the money.” Later, after outcry from allies of the president, Mulvaney denied he said anything of the sort. The White House did not respond to a request for comment.

—with additional reporting by Adam Rawnsley.