Bill Taylor, the top U.S. diplomat in Ukraine, testified on Wednesday that he became increasingly alarmed as it became clear that U.S. military aid was conditioned on launching investigations into former Vice President Joe Biden and the 2016 election.

Taylor and George Kent, the deputy assistant secretary of state, were the first witnesses called to testify in the impeachment inquiry of President Donald Trump before the House Intelligence Committee. The committee is examining whether Trump abused his power by encouraging the Ukrainian government to interfere in the 2020 election.

Taylor said he understood that a White House visit by Ukraine President Volodymyr Zelensky was conditioned on the investigations. He later came to understand, through Gordon Sondland, the U.S. ambassador to the European Union, that military aid was also on the line.

“The White House meeting was one thing,” Taylor said. “Security assistance was much more alarming.”

Much of Taylor’s testimony was previously disclosed in a transcript of his closed-door deposition on Oct. 22. However, he did offer new information about a July 26 conversation at a restaurant between Sondland and a member of Taylor’s staff. The staff member overheard Sondland on the phone with Trump discussing “the investigations,” Taylor said. After the call, the staffer asked what the president thought of the Ukraine situation.

“Ambassador Sondland responded that President Trump cares more about the investigations of Biden,” Taylor testified.

In his opening statement, Taylor laid out how U.S. policy toward Ukraine became split over the summer between a “regular channel” and an “irregular channel.” The latter channel, which included Sondland and Rudy Giuliani, the president’s attorney, focused on pressuring the Ukrainians to give a CNN interview about an investigation into Burisma, the Ukrainian gas company whose board included Hunter Biden, the former vice president’s son.

Taylor said he urged Sondland to push back on the arrangement, arguing that it would be “crazy” to condition support for Ukraine on political investigations.

In response to a question from Committee Chairman Adam Schiff, Taylor argued that Ukraine is on the front line of a conflict with Russia that threatens the stability of Europe. He argued that undermining the relationship with Ukraine poses a risk to U.S. national security.

“The Russians are violating all of the rules, treaties, and understandings that they committed to that actually kept the peace in Europe for nearly 70 years,” Taylor said. “If we don’t push back on those violations then that will continue. That affects us. That affects the world we live in, that our children and grandchildren will grow up in.”

In his opening statement, Schiff laid out a summary of the president’s efforts to lean on Ukraine to launch an investigation of Burisma and the circumstances around the 2016 election.

“If this is not impeachable conduct, what is?” Schiff asked.

Devin Nunes, the ranking Republican on the committee, argued that Democrats were seeking a do-over of the probe into Russian interference in the 2016 election. He called the hearing a “theatrical performance” staged by Democrats to damage the president, advising the witnesses that they had been cast in a “low-rent Ukrainian sequel” to the Russia probe.

“This spectacle is doing great damage to our country,” Nunes said. “It is nothing more than an impeachment process in search of a crime.”