WASHINGTON     -   The Democratic-led impeachment inquiry of President Donald Trump moves ahead on Thursday after an opening day of public testimony that linked Trump to a pressure campaign to force Ukraine to conduct investigations that would benefit him politically.

The first day of televised hearings, following weeks of closed-door interviews about Trump’s dealings with Ukraine, gave a potential audience of tens of millions of Americans their first look at a probe that has ignited partisan passions ahead of the 2020 presidential campaign.

William Taylor, the acting ambassador to Ukraine, offered a new disclosure about the Republican president’s keen interest in getting Ukraine to investigate Democratic political rival Joe Biden, saying a member of his staff overheard a July 26 phone call in which Trump asked about those investigations.

After the call between Trump and Gordon Sondland, a former political donor appointed as a senior diplomat, the staff member asked Sondland what Trump thought about Ukraine, Taylor said.

“Ambassador Sondland responded that President Trump cares more about the investigations of Biden, which Giuliani was pressing for,” Taylor testified, referring to Trump’s personal lawyer, Rudy Giuliani.

Trump told reporters at a White House news conference after the hearing ended that he knew “nothing” about the call with Sondland. “It’s the first time I heard it,” said Trump, who has denied any wrongdoing.

David Holmes, a Taylor aide subpoenaed to testify behind closed doors on Friday in the impeachment inquiry, is the staffer who overheard the call that Sondland made to Trump from Ukraine, said a person familiar with the issue.

Republican lawmakers called Taylor’s account hearsay and noted Ukraine’s president has not said he felt pressured by Trump. The hearings may pave the way for the Democratic-led House of Representatives to approve articles of impeachment - formal charges - against Trump.

That would lead to a trial in the Senate on whether to convict Trump of those charges and remove him from office. Republicans control the Senate and have shown little support for Trump’s removal. The focus of the inquiry is a July 25 phone call in which Trump asked Ukrainian President Volodymyr Zelenskiy to open a corruption investigation into Biden and his son Hunter, and into a discredited theory that Ukraine, not Russia, meddled in the 2016 U.S. election. Hunter Biden had been a board member for a Ukrainian energy company called Burisma.

Democrats are looking into whether Trump abused his power by withholding $391 million in U.S. security aid to Ukraine - a vulnerable U.S. ally facing Russian aggression - as leverage to pressure Kiev into conducting the investigations. The money - approved by the U.S. Congress to help Ukraine combat Russia-backed separatists in the eastern part of the country - was later provided to Ukraine. Wednesday’s hearing, held in an ornate hearing room packed with journalists, lawmakers and members of the public, was the first step in a new public phase of the impeachment inquiry as Democrats and Republicans each try to make their case to the public.

Ratings for the hearing are expected to be available on Thursday, giving both parties their first reading on how interested the public is. The inquiry is being conducted as the 2020 presidential campaign begins to gather steam.