Washington: He stood on one side of a war-damaged bridge in Ukraine staring across at Russian-backed forces and saw the real-world consequences of President Donald Trump’s efforts to advance a personal agenda. “More Ukrainians,” he said, “would undoubtedly die.”

Recalling that moment during explosive testimony Tuesday, William B. Taylor Jr., the top American diplomat in Ukraine, laid out in visceral terms the stakes of what he saw as an illegitimate scheme to pressure the Kiev government for political help by suspending US security aid.

In by far the most damning account yet to become public in the House impeachment inquiry, Taylor described a president holding up $391 million in aid for the clear purpose of forcing Ukraine to help incriminate Trump’s domestic rivals. Trump’s actions, he testified, undercut US allies desperately fighting to stave off Russian aggression.

Without the money that Trump held up, Taylor said, Ukraine would find it harder to defend itself in the face of Moscow’s attempt to redraw the boundaries of Europe through force of arms.

“If Ukraine succeeds in breaking free of Russian influence, it is possible for Europe to be whole, free, democratic and at peace,” Taylor said in his opening statement to House investigators, which was provided to reporters after he delivered it behind closed doors. “In contrast, if Russia dominates Ukraine, Russia will again become an empire, oppressing its people and threatening its neighbours and the rest of the world.”

Taylor’s vivid depiction illustrated the differences between the impeachment inquiry against Trump and the ones that consumed Presidents Richard Nixon and Bill Clinton. While the Watergate and Monica Lewinsky cover-ups involved the integrity of America’s democracy and system of justice, the Ukraine scandal also extends to matters of life and death, as well as geopolitics on a grand scale.

Taylor’s testimony could make it harder for Republicans to brush off Trump’s actions as unimportant or distorted by partisan foes. Defending Ukraine against Russian encroachment, much like defending the United States’ Kurdish allies against Turkey, has been a high priority for many Republicans, who complained that President Barack Obama did not stand up to Moscow aggressively enough.

Taylor brought to the House hearing a 50-year resume of public service, starting as a cadet at the US Military Academy at West Point and an infantry officer with the 101st Airborne Division in Vietnam. He served every administration, Republican and Democrat, since President Ronald Reagan, culminating with a posting as ambassador to Ukraine under President George W. Bush. And he was recruited last spring by Mike Pompeo, Trump’s secretary of state, to return to Kiev to replace Marie L. Yovanovitch, the ambassador tarred by Trump’s camp as an adversary.

The chain of events that Taylor laid out in his testimony suggested a clear quid pro quo between $391 million in suspended assistance and Trump’s demands that Ukraine investigate former Vice-President Joe Biden as well as a debunked conspiracy theory involving Ukrainian help for Democrats in the 2016 election.

Yet in the publicly released portion of his testimony, Taylor neither described any direct conversation with Trump nor made any reference to documents or recordings that would explicitly implicate the president. Instead, he provided a road map for investigators by quoting others around Trump describing his actions and statements.

“President Trump has done nothing wrong — this is a coordinated smear campaign from far-left lawmakers and radical unelected bureaucrats waging war on the Constitution,” Stephanie Grisham, the White House press secretary, said in a statement. “There was no quid pro quo. Today was just more triple hearsay and selective leaks from the Democrats’ politically motivated, closed-door, secretive hearings.”

Taylor’s testimony once again focused attention on Trump’s unusual relationship with President Vladimir Putin’s Russia. Unlike most leaders in both parties, Trump has rarely expressed much criticism of Putin or his aggression against his neighbours, at one point even suggesting that he could accept Russia’s annexation of Crimea, which it seized from Ukraine through force in 2014.

Trump went further than Obama by providing lethal military assistance to Ukraine to defend itself against Russia but privately echoed Putin’s line about the Ukrainians being untrustworthy and corrupt. By holding up the $391 million in aid allocated by Congress, Trump essentially reversed his own policy and angered lawmakers of both parties, who pressured him into releasing the money last month.

In his 14-page opening statement, bristling with indignation yet chock-full of dates, facts and quotes, Taylor described “two channels of US policymaking and implementation, one regular and one highly irregular,” run largely by the president’s personal attorney, Rudy Giuliani, as well as others like Gordon D. Sondland, ambassador to the European Union.

He recalled being stunned to learn during a secure video conference call July 18 that the aid to Ukraine had been put on hold with no explanation other than that “the directive had come from the president to the chief of staff to” the Office of Management and Budget.

“I and others sat in astonishment,” he testified. “The Ukrainians were fighting the Russians and counted on not only the training and weapons, but also the assurance of US support.”

No one told the Ukrainians at first, and Taylor recalled meeting with President Volodymyr Zelenskiy in Kiev on July 26, the day after Trump pressured the newly elected Ukrainian leader on the telephone to investigate Biden and the 2016 election conspiracy theory.

After the meeting, he joined Zelenskiy and Kurt D. Volker, the State Department special envoy for Ukraine, on a trip to northern Donbas, the front line of the conflict with Russian-backed separatists, where they were briefed by the commander of Ukrainian forces.

“The commander thanked us for security assistance, but I was aware that this assistance was on hold, which made me uncomfortable,” Taylor said. “Ambassador Volker and I could see the armed and hostile Russian-led forces on the other side of the damaged bridge across the line of contact. Over 13,000 Ukrainians had been killed in the war, one or two a week. More Ukrainians would undoubtedly die without the US military assistance.”

As weeks went by without a resolution of the aid impasse, Taylor said he began preparing to resign.

Before he could resign, congressional leaders intervened and persuaded Trump to lift the suspension. Taylor still serves as the top diplomat in Ukraine. For now.