WASHINGTON • The White House violated federal law by withholding security aid approved by lawmakers for Ukraine, a non-partisan congressional watchdog said, in a blow to United States President Donald Trump as the Senate formally opened the trial on whether to remove him from office.

The Democrat-led House of Representatives on Wednesday sent the Senate the two charges it passed last month accusing Mr Trump of abuse of power and obstruction of Congress arising from his dealings with Ukraine, clearing the way for only the third impeachment trial of a president to begin in earnest next week.

The abuse of power cited by the House included Mr Trump's withholding of US$391 million (S$526 million) passed by Congress in security aid for Ukraine, a move aimed at pressuring Kiev into investigating Mr Joe Biden, Mr Trump's possible Democratic opponent in the Nov 3 presidential election.

The US$391 million was approved by lawmakers to help Ukraine combat Russia-backed separatists in the eastern part of the country.

"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 Government Accountability Office (GAO) on Thursday concluded.

An arm of Congress, the GAO is viewed as a top auditing agency for the federal government that advises lawmakers and various government entities on how taxpayer dollars are spent.

On Thursday, Democrat Adam Schiff, who heads a team of seven House members who will serve as prosecutors in the trial, formally presented the articles of impeachment on the Senate floor, reading through the allegations against the Republican President. It was unclear, however, how or even if the GAO's decision would figure in Mr Trump's trial in the Republican-led Senate.

REUTERS