House Democrats called Taylor and George Kent, a deputy assistant secretary in the State Department, as their opening witnesses in the public impeachment hearings because the two veteran diplomats have made the most detailed and explicit allegations against the president and his top lieutenants. The Democrats’ case centers on a quid pro quo—all but acknowledged by top White House officials—in which the Trump administration held up crucial U.S. aid to Ukraine for a public commitment by Zelensky to investigate former Vice President Joe Biden—a potential Trump foe in 2020—and an energy company that appointed his son Hunter to sit on its board.

Republicans defending the president have complained that much of the Democrats’ case for impeachment has relied on second- or thirdhand information far removed from Trump. This phone call, however, involves the president directly and offers more evidence that he sought to use U.S. policy toward Ukraine for his own political interests.

In questioning after Taylor’s opening statement, Intelligence Committee Chairman Adam Schiff asked the ambassador whether Sondland was saying that Trump cared more about the investigations of Biden “than he does about Ukraine.”

“Yes, sir,” Taylor replied.

The hearings that began this morning in the ornate Ways and Means Committee room on Capitol Hill will introduce Americans for the first time to a cast of senior diplomats and White House officials who have come forward to report alleged wrongdoing following an initial complaint by a still-anonymous whistle-blower in the U.S. intelligence community. Democrats are hoping that the credibility of veteran public servants like Taylor, a Vietnam veteran who has served in the State Department for nearly 35 years, and Kent, another senior official, who comes from a family of diplomats, will sway both the viewing public and ultimately the Senate Republicans who could decide whether to remove Trump from office.

The president has labeled nearly all of the Democrats’ witnesses, even officials he has named to their posts, as “Never Trumpers.” At the outset, however, both Kent and Taylor stressed that they had worked for presidents of both parties and were not pursuing an agenda against Trump.

“I am not here to take one side or the other or to advocate for one particular outcome of these proceedings,” Taylor said.

Read: Trump’s first impeachment win

Trump’s defenders have denounced the process as a “sham” and tried to disrupt this morning’s hearing from its opening minutes with procedural inquiries. Representative Devin Nunes of California, the top Republican on the Intelligence Committee and a staunch ally of the president, accused Democrats of running a casting call for witnesses with their initial round of closed-door depositions in the Capitol basement. He dismissed Taylor and Kent as “witnesses deemed suitable for television by the Democrats.”