The U.S. Government Accountability Office released Thursday a decision finding that the White House's Office of Management and Budget violated the law when it withheld military aid to Ukraine.

The state of play: The decision from the GAO, an independent government agency, comes just hours before the Senate will kick off President Trump's impeachment trial over his administration's actions on Ukraine.

The big picture: The GAO found that the OMB violated the 1974 Impoundment Control Act, which requires that the White House and its agencies disburse funds appropriated by Congress as directed by the legislative branch.

The GAO probe was initially requested last year by Sen. Chris Van Hollen (D-Md.).

He told Roll Call that while the abuse of power article of impeachment against Trump does not directly reference a violation of the ICA, it remains "all part of the picture that's being painted."

Michael Duffey, a political appointee at OMB who ordered the hold on Ukraine aid 90 minutes after Trump's phone call with Ukraine's president, is among the witnesses Democrats want to call at the impeachment trial.

What it means: The only recourse the GAO has for a violation of the ICA is to sue the administration to release the funds, per Roll Call. In this case, the withheld aid was already released in September.

Van Hollen has proposed an amendment to the ICA that would require OMB to be more transparent in its decisions to withhold funds.

What they're saying:

"Faithful execution of the law does not permit the president to substitute his own policy priorities for those that Congress has enacted into law. OMB withheld funds for a policy reason, which is not permitted under the Impoundment Control Act (ICA). The withholding was not a programmatic delay. Therefore, we conclude that OMB violated the ICA."

— GAO report

The other side: Rachel Semmel, the OMB's communications director, said in a statement, "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."

Read the full decision.

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