William Taylor, the top U.S. diplomat in Ukraine, told House impeachment investigators he was told President Trump cared more about investigations into his political rivals more than he cared about relations with Ukraine.

Taylor, the acting ambassador to Ukraine, was one of two kick-off witnesses in the public phase of the House impeachment inquiry, which centers on whether Trump abused the power of his office by withholding $391 million in military aid to the former Soviet republic in exchange for political dirt on one of the candidates for the 2020 Democratic presidential nomination.

He said a member of his staff heard U.S. Ambassador to the European Union Gordon Sondland talking on the phone with Trump during which Sondland told him Ukraine was ready to go ahead with investigations of former Vice President Joe Biden, his son, Hunter, and a debunked conspiracy theory about Ukraine involvement in the 2016 U.S. presidential election. The aide asked Sondland what the president thought of Ukraine, and the ambassador responded, “President Trump cares more about the investigations of Biden.”

The incident was not part of Taylor’s closed-door deposition last month, he said, because he was not aware of it at the time.

Trump denied knowledge of the call, telling reporters, "First time I heard it."

Republicans tried to spin the testimony, accusing Taylor of being a “star witness” in the impeachment saga. He responded by saying he was just there to lay out the facts.

Asked whether the president committed an impeachable offense, Taylor responded: “I’m not here to… decide about impeachment. … This is your job.”

In his opening statement, Taylor outlined why it was necessary for the U.S. to provide military assistance to Ukraine, saying it was in the U.S. national interest to keep Russia from making further incursions into Ukraine territory.

Taylor discovered on his arrival in Kyiv that U.S. foreign policy was being conducted on two tracks: an official structure that reported to the State Department and a backchannel operation promoted by Trump attorney Rudy Giuliani that was at odds with official positions.

“I found this a confusing and unusual arrangement for making U.S. policy toward Ukraine,” he said.

Trump dismissed the proceedings, saying he's too busy to watch the hearings during an Oval Office meeting with Turkey's president.

“I’m too busy to watch it. It’s a witch hunt, it’s a hoax, I’m too busy to watch it. So, I’m sure I’ll get a report,” Trump told reporters.