But a 1974 law that governs budget procedure within the government "does not permit OMB to withhold funds for policy reasons", said Thomas Armstrong, general counsel for the watchdog Government Accountability Office.

Previously, White House budget office lawyers had characterized the funding hold as a "programmatic delay", in which "operational factors unavoidably impede" the obligation of funds despite "reasonable and good faith efforts to implement the program", using GAO definitions. "Therefore, we conclude that the OMB violated the ICA [Impoundment Control Act]".

The O.M.B. said they don't agree with the G.A.O report, released Thursday, which claims this administration violated the law by withholding aid from the Ukraine.

House Appropriations Chair Nita Lowey of NY said that the GAO "confirmed what congressional Democrats have understood all along: President Trump abused his power and broke the law by withholding security assistance to Ukraine".

The nonpartisan Government Accountability Office has confirmed what Congressional Democrats have understood all along: President Trump abused his power and broke the law by withholding security assistance to Ukraine.

While the agency's assessment was a setback to Mr Trump, it was unclear how or even if it would figure in his trial in the Republican-led Senate given that key issues such as whether witnesses will appear or new evidence will be considered remain up in the air.

In practical terms, the GAO may have broad investigatory powers, but it lacks enforcement authority: in a case like this one, it could go to court to force the White House to release the withheld funds. GAO said the withholding was an illegal "deferral" of money appropriated by Congress and ran afoul of a Nixon-era law aimed at ensuring funds are spent according to lawmakers' intent.

"President Trump and his top aides refused to cooperate with this independent investigation, just as they obstructed the impeachment investigation conducted by the House of Representatives". If the president seeks to delay or rescind spending, the report states, the law requires him to notify Congress. For another, there's fresh evidence that Trump's extortion scheme in Ukraine did, in fact, break the law.

While the letter freezing the funds was initially signed by Mark Sandy, a career OMB official, it was renewed several times by a political appointee, Michael Duffey, which budget veterans have said is highly unusual.

The report isn't the sexiest Ukraine-related tidbit circulating these days; far more attention is being paid to the latest accusations from Lev Parnas, the Ukrainian American who was part of Rudolph W. Giuliani's merry band of pranksters trying to dig up dirt against former Vice President Joe Biden.

The White House didn't immediately return a request for comment.

What the GAO has done is "establish conclusively that the Trump administration violated the law when they withheld money".

GAO also found in 2014 that the Obama administration broke the law in exchanging five Taliban commanders for a captured USA soldier without giving Congress 30 days notice.