The Trump administration broke the law by withholding congressionally approved military aid to Ukraine last summer "for a policy reason," a top government watchdog said Thursday in a scathing report.
The Government Accountability Office's report came a day after the House of Representatives sent articles of its impeachment of President Donald Trump to the Senate for conduct related to holding back that aid.
Trump refused to release the funds to Ukraine at the same time he was pressuring that country's new president to announce investigations of former Vice President Joe Biden and of Biden's son Hunter, who had served on the board of a Ukraine gas company. Joe Biden is the current front-runner for the Democratic presidential nomination.
The funds were only released after the block on the aid became publicly known, sparking the congressional probe which led to the Republican president's impeachment by the Democratic-controlled House.
The GAO report said that the Office of Management and Budget cited "a policy reason" for withholding $214 million in funds appropriated by Congress to the Defense Department for security assistance to Ukraine.
But a policy reason "is not permitted under the Impoundment Control Act" to withhold funds appropriated by Congress, GAO said.
"The withholding was not a programmatic delay. Therefore, we conclude that OMB violated the ICA."
"Faithful execution of the law does not permit the President to substitute his own policy priorities for those that Congress has enacted into law," the report said.
The agency noted that the Constitution "specifically vests Congress with the power of the purse."
And the report said that Trump, like all other presidents, "is not vested with the power to ignore or amend any such duly enacted law."
"Faithful execution of the law does not permit the President to substitute his own policy priorities for those that Congress has enacted into law."
House Speaker Nancy Pelosi, D-California, said, "The OMB, the White House, the administration, broke — I'm saying this —- broke the law."
OMB spokeswoman Rachel Semmel, said, "We disagree with GAO's opinion."
"OMB uses its apportionment authority to ensure taxpayer dollars are properly spent consistent with the President's priorities and with the law," Semmel said.
A senior administration official, speaking on the condition of anonymity, said, "GAO's findings are a pretty clear overreach as they attempt to insert themselves into the media's controversy of the day."
Trump's trial formally began in the Senate chamber later Thursday. But GAO General Counsel Thomas Armstrong said its report was not deliberately timed to release at the same time as the trial.
"Our legal decisions are issued when we have completed all of our research and are ready to come to a sound conclusion," Armstrong said in a response to CNBC's inquiry about the timing of the release.
"There was no coordination of timing with any entity outside of GAO," Armstrong said.
Sen. Chris Van Hollen, a Maryland Democrat who had asked GAO to investigate the issue, called the report a "bombshell legal opinion."
The report "demonstrates, without a doubt, that the Trump Administration illegally withheld security assistance from Ukraine," Van Hollen said.
"The publicly available evidence also shows that the President himself ordered this illegal act."
The senator also said, "This violation of the law reflects a contempt for the Constitution and was a key part of his corrupt scheme to abuse the power of the presidency for his personal political purposes. The GAO's independent findings reinforce the need for the Senate to obtain all relevant documents and hear from key fact witnesses in order to have a fair trial."
House Appropriations Committee Chairwoman Rep. Nita Lowey, D-New York, said in a statement, "Congress makes funding decisions, and the Trump Administration's illegal impoundment of these vital national security funds was a brazen assault on the checks and balances inherent to our democracy," Lowey said.
"Given that this illegal conduct threatened our security and undermined our elections, I feel even more strongly that the House has chosen the right course by impeaching President Trump. No one is above the law," Lowey said.
Pentagon spokesman Jonathan Hoffman said, "Our goal with regard to Ukraine aid, has always continued to be, to ensure that anti-corruption measures were in place and that the money would be well spent."
"To ensure that our European allies were additionally helping with it and to ensure that this assistance would be beneficial militarily," Hoffman said.
"So, we went through that process to make a determination on the aid. We also looked to make sure that the aid was going to get out by the fiscal year, as required by Congress and other than a very small part, that did happen. The aid got out with no detriment to our national security."
Hoffman also said, "All of the aid has been obligated and is out."