The United States Senate acquitted President Donald Trump Wednesday on his impeachment case, but was denied the full backing of Republicans as Senator Mitt Romney became the first lawmaker in US history to vote for the conviction of a president from his own political bloc.

After five months of court drama and revelations about the commander in chief's secret dealings with Ukraine, a divided US Senate dropped charges of abuse of power against Trump and obstructed the House of Representatives to support his bid for reelection, bringing a bitter impeachment trial to its anticipated closure.

Trump was acquitted of the first charge of abuse of power by a vote of 52 to 48, as Romney voted with Democrats. The Senate found Trump not guilty by a party-line 53 to 47 vote on a second charge of obstructing Congress.

Many had long predicted that Trump will be acquitted: a two-thirds vote is needed to impeach a president from office, but the Utah senator's striking reproach brought bipartisan momentum to an indictment that the president's party had otherwise steadfastly resisted.

In December, Democrats accused Trump of pressuring Ukraine to tarnish a potential political adversary in the White House. Trump will become the first impeached president to run for another term in November.

The Senate deliberated in its landmark vote not to oust America's 45th president from power on charges stemming from his relations with Ukraine. He would have had to hand over his office to Vice President Mike Pence, had he been found guilty of the charges.

It was a president's third impeachment trial and the third acquittal in American history and it culminated the way it started: with Democrats and Republicans fighting tooth and nail.

They disagreed over the behavior of Trump and his capacity to run the country, even as some members of his own political organization admitted the fundamental accusations that undergrounded the charges that he sought to pressure Ukraine to smear his political foes.

Romney, a 2012 Republican presidential candidate, made an emotional statement ahead of the vote in which he strongly lambasted the efforts of Trump to press Ukraine to probe Joe Biden, a Democratic presidential candidate, by denying military aid.

Trump himself did not address his acquittal directly, but he announced moments later on Twitter that he would issue a public statement at the White House on Thursday about what he described "our country's victory on the Impeachment Hoax." The president then posted an attack ad against Romney that labeled him a "hidden asset" of the Democrat.