WASHINGTON >> The House of Representatives opened historic impeachment hearings Wednesday and heard a senior American diplomat reveal startling new testimony that drew President Donald Trump closer to the center of the effort to pressure Ukraine to investigate former Vice President Joe Biden.

In a nationally televised hearing in the House Ways and Means Committee room across from the Capitol, William Taylor, the top American diplomat in Ukraine, brought to life Democrats’ allegations that Trump has abused his office by trying to enlist a foreign power to help him in an election. Taylor testified to the House Intelligence Committee, which is leading the inquiry, that his aide was told in July that Trump cared more about “investigations of Biden” than he did about Ukraine.

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The revelation, as Congress embarked on only the third set of presidential impeachment hearings in modern times, tied Trump more directly into what Taylor described in vivid detail as a “highly irregular” effort to place the president’s political interests at the center of American policy toward Ukraine.

“I don’t think President Trump was trying to end corruption in Ukraine,” said Rep. Jim Himes, D-Conn., encapsulating Democrats’ case. “I think he was trying to aim corruption in Ukraine at Vice President Biden and at the 2020 election.”

The proceedings pushed into the public gaze an epic clash between Trump and Democrats over impeachment that has shifted into high gear less than a year before the presidential election. In the first impeachment hearing on Capitol Hill in more than two decades, Taylor and another veteran diplomat, George Kent, sketched out, in testimony by turns cinematic and dry, a tale of foreign policymaking distorted by a president’s political vendettas with a small country facing Russian aggression caught in the middle.

“If this is not impeachable conduct,” demanded Rep. Adam Schiff, D-Calif., the chairman of the committee, “what is?”

Democrats toiled to make their case to a deeply divided nation that Trump had put the integrity of the 2020 election at risk — by withholding vital security assistance for Ukraine’s war with Russia to try to extract a political advantage for his reelection campaign.

Showing no sign of doubts, Trump’s Republican defenders raged against an impeachment process they called unfair and illegitimate, dismissing Taylor and Kent — who between them have 70 years of experience as public servants under presidents of both parties — as part of a “politicized bureaucracy” who were offering nothing more than hearsay and supposition, rather than evidence of impeachable conduct.

“The American people see through all this,” said Rep. Jim Jordan, R-Ohio. “They understand the facts support the president. They understand this process is unfair. And they see through the whole darn sham.”

At the White House, Trump sought to project an air of confidence in the face of an existential threat to his presidency. Before a working meeting with President Recep Tayyip Erdogan of Turkey, Trump told reporters of the impeachment hearing: “It’s a witch hunt. It’s a hoax. I’m too busy to watch it.”

But even so, Trump was busy all day retweeting allies commenting on the proceedings and defending him. His reelection campaign blasted out a fundraising solicitation accusing Democrats of “playing a sick game.” And the Republican National Committee circulated memes making fun of the witnesses as gossips who lacked firsthand information.

Even as the public recitation of facts unfolded in the hearing room, there were signs that Democrats’ investigation was still expanding. Investigators scheduled depositions with David Holmes, an official in the U.S. Embassy in Kyiv, and Mark Sandy of the Office of Management and Budget for Friday and Saturday. According to an official involved in the inquiry, Holmes was the aide Taylor referred to in his new testimony, who informed Taylor about Trump’s singular interest in investigating Joe Biden and his son, Hunter Biden, who served on the board of a Ukrainian natural gas producer from 2014 to 2019.

Taylor said a member of his staff overheard a telephone conversation in which the president mentioned “the investigations” to Gordon Sondland, the United States ambassador to the European Union, who told Trump “that the Ukrainians were ready to move forward.” The conversation took place just one day after Trump personally pressed Ukraine’s new president in a phone call to investigate Bidens and unproven allegations that Ukraine conspired with Democrats to interfere in the 2016 election.

When the staff member inquired after the call what the president thought about Ukraine, Sondland “responded that President Trump cares more about the investigations of Biden, which Giuliani was pressing for,” in Taylor’s telling. Rudy Giuliani, the president’s personal lawyer, led what Taylor called a “highly irregular” policymaking channel on Ukraine that ran counter to goals of long-standing American policy.

The episode was not included in Taylor’s interview with impeachment investigators last month because, he said, he was not aware of it at the time. But the new disclosure promises to figure prominently when Sondland appears for his own public testimony next week.

The revelation came as Taylor recounted publicly what he had already told impeachment investigators privately about how he had discovered that Trump was conditioning “everything” about the United States relationship with Ukraine — including needed military aid and a White House meeting for Ukraine’s president — on the country’s willingness to commit publicly to investigations of his political rival. His testimony made it clear that the Ukrainians were well aware of the prerequisite at the time.

Asked by a Democratic lawyer if he had ever seen “another example of foreign aid conditioned on the personal or political interests of the president of the United States,” Taylor, in a deeply sonorous voice that echoed through the hearing room as he delivered his remarks, said: “I have not.”

In his opening statement, Kent said he had concluded by mid-August that Giuliani’s efforts to pressure President Volodymyr Zelenskiy of Ukraine to open investigations into Trump’s rivals “were now infecting U.S. engagement with Ukraine, leveraging President Zelenskiy’s desire for a White House meeting.”

Kent also assailed what he called a “campaign to smear” American officials serving in Ukraine, which succeeded with the ouster of Marie Yovanovitch, the former U.S. ambassador to Ukraine.

Over the coming 10 days, Democrats hope to lay out a case that will capture the public’s attention and convince a majority of Americans that Trump’s actions are worthy of the Constitution’s gravest reprimand, possible removal from office.

Determined to seize what is plainly their best chance to capture the attention of the American public, Schiff, the committee’s chairman, laid out the stakes. He invoked the words of Mick Mulvaney, the acting White House chief of staff, who defiantly told reporters to “get over it” when questioned about conditioning military aid to Ukraine to investigations Trump wanted.

“If he sought to condition, coerce, extort or bribe an ally into conducting investigations to aid his reelection campaign, and did so by withholding official acts — a White House meeting or hundreds of millions of dollars of needed military aid — must we simply ‘get over it’?” Schiff asked. “Is this what Americans should now expect from their president?”

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