During previous Democratic investigations, the White House has moved to block testimony by a string of current and former staffers by citing executive privilege. The administration even asked Corey Lewandowski not to testify to certain matters, even though he’s never been an employee of the executive branch. But these maneuvers required that the people involved be willing, for whatever reason, to honor the White House’s request.

Yovanovitch and Sondland, also for whatever reason, have decided they won’t do that. What’s notable is that both of them are still employed by the State Department, which can ask them not to testify, but cannot force them not to.

David A. Graham: What happened in Ukraine?

Though she was recalled as ambassador to Ukraine, Yovanovitch is a career Foreign Service officer and remains at the State Department. It’s no surprise she doesn’t feel much reason to honor the president’s wishes: She was recalled after Trump’s personal lawyer Rudy Giuliani campaigned for her removal; a federal indictment of two Giuliani associates unsealed Thursday also showed how they’d asked former Representative Pete Sessions to write a letter calling for her ouster, after making large political donations. She’s expected to testify to Giuliani’s machinations in Ukraine, including attempting to dig up dirt on the Biden family.

It’s less clear why, as Sondland’s lawyer said in a statement, “notwithstanding the State Department’s current direction to not testify, Ambassador Sondland will honor the Committees’ subpoena” and appear on October 17, or whether he might decline to answer certain questions. Sondland was originally scheduled to testify on Wednesday, but did not show. Unlike Yovanovitch, he is a political appointee, given his title after helping raise funds for the Trump campaign. Sondland is a hotelier in Oregon.

Sondland’s name appeared in a series of text messages handed over to the House by Kurt Volker, who testified last week, shortly after being fired as an envoy to Ukraine. Those questions showed that American and Ukrainian officials believed that there was a quid pro quo in place, in which Ukraine must investigate the Bidens and an arcane 2016-election conspiracy theory in return for military aid and a meeting with the president. Perhaps Sondland believes his testimony will clear his name, or Trump’s.

David A. Graham: The mystery of the Ukraine-call transcript

Motives aside, testimony from Sondland and Yovanovitch, like that of Volker, could influence future witnesses. The House has invited a slew of other current executive-branch employees to testify as well, including William Taylor, now the current top diplomat in Ukraine. In the messages Volker produced, Taylor seemed to be consciously creating a paper record of conversations. “Are we now saying that security assistance and WH meeting are conditioned on investigations?” he said in one message. Later, Taylor wrote, “I think it’s crazy to withhold security assistance for help with a political campaign.” Whether these officials testify will help determine whether a dam is breaking or some water has merely spilled over the top.