The top U.S. diplomat in Ukraine, William Taylor, is testifying in the House impeachment inquiry’s first public hearing Wednesday.

In his prepared opening remarks, Taylor said withholding military aid to Ukraine in exchange for a political investigation is “crazy,” and advised to “stay clear” of becoming entangled in foreign investigations.

He testified that the President of Ukraine, Volodymyr Zelenskyy, was eager to gain an Oval Office meeting with President Donald Trump. According to Taylor, several officials led by Trump attorney Rudy Giuliani, used the meeting as leverage to pressure him to open an investigation into Trump’s political rival, as well as a debunked conspiracy theory about the 2016 election.

“By mid-July it was becoming clear to me that the meeting President Zelenskyy wanted was conditioned on the investigations of Burisma and alleged Ukrainian interference in the 2016 U.S. elections,” Taylor said in his opening statement.

Former Vice President Joe Biden‘s son sat on the board of Burisma, a Ukraine-based gas company, at the time. Trump believes that while Biden was Vice President, he withheld aid and pressured Ukraine to fire its then-top prosecutor because he was investigating Burisma on tax-related charges. However, the prosecutor was widely seen as corrupt and the investigation was no longer active at that point.

Taylor received several text messages and phone calls from a few ambassadors in the days leading up to Trump’s July 25 phone call with Zelenskyy. He said that in a July 20 phone call with Gordon Sondland, the U.S. ambassador to the European Union, Sondland suggested to Zelenskyy that he use the phrase, “I will leave no stone unturned,” in response to Trump’s investigation request.

He added that he did not read the transcript of the call until it was made public in September, but had become increasingly concerned about the separate channel of U.S. foreign policy in Ukraine.

“On August 16, I exchanged text messages with Ambassador Volker in which I learned that Andriy Yermak, a senior advisor to President Zelenskyy, had asked that the United States submit an official request for an investigation into Burisma’s alleged violations of Ukrainian law, if that is what the United States desired,” Taylor said. “A formal U.S. request to the Ukrainians to conduct an investigation based on violations of their own law struck me as improper, and I recommended to Ambassador [Kurt] Volker that we ‘stay clear.'”

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Sondland told him on Sept. 1 that Trump wanted Zelenskyy to announce an investigation into Burisma and the 2016 election publicly, in order to receive both a White House meeting and the blocked U.S. military aid.

During that conversation, Taylor said Trump “should have more respect for another head of state,” but also “suggested the possibility that the Ukrainian Prosecutor General, rather than President Zelenskyy, would make a statement about investigations.”

Taylor, who only accepted the position on the condition of continued U.S. support to Ukraine, concluded his opening statements by emphasizing the need to prevent Ukraine’s “young nation” from Russian offensives.