WASHINGTON — President Trump’s White House decision to withhold vital military assistance to Ukraine violated U.S federal law, a Congressional watchdog announced Thursday morning.

The Government Accountability Office, a non-partisan federal watchdog, noted that “Faithful execution of the law does not permit the President to substitute his own policy priorities for those that Congress has enacted into law.” And yet, the GAO found that was precisely what President Donald Trump’s White House did.

The White House quickly shot back at the GAO, saying that the charge was an attempt by the watchdog to insert itself into the “media’s controversy of the day,” according to the Washington Post.

“We disagree with GAO's opinion,” the White House Office of Management and Budget said in a statement provided to VICE News. “OMB uses its apportionment authority to ensure taxpayer dollars are properly spent consistent with the President's priorities and with the law."

The announcement will pour gasoline on the raging fire of Trump’s impeachment, which just arrived in the Senate for a trial that will begin next week. The House impeached Trump in December for abusing his office by pressuring Ukraine to announce an investigation of his 2020 Democratic rival, former vice president Joe Biden.

Trump withheld $391 million in aid to Ukraine in July of last year in what Democrats argue was a pressure tactic to get Ukraine to announce the investigation. The White House tried to argue that that was standard operating procedure.

But in July, Trump personally asked Ukrainian President Volodymyr Zelensky to “look into” former Vice President Joe Biden and his son Hunter, who’d previously sat on the board of a Ukrainian energy company.

Emails that were made public in December show that Trump directed his budget office to withhold aid to Ukraine less than two hours after Trump got off the phone with Zelensky.

The GAO found in its report that the White House had violated the Impoundment Control Act, which lays out the specific mechanism through which the executive branch can request that Congress reconsider the way it’s allocated funds.

Minutes after the report dropped, Democrats pounced on it. The report “establishes beyond a doubt that the Trump administration violated the law when it withheld badly-need security funds for the Ukraine,” Senator Chris Van Hollen of Maryland said in a video posted to Twitter.

“The GAO opinion is forceful and unambiguous,” said Democratic Sen. Patrick Lahey of Vermont in a statement posted on social media. “When President Trump froze congressionally appropriated military aid to Ukraine, he did so in violation of the law and the Constitution.”

Read the GAO’s full report here: