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Republicans have been saying that if former National Security Adviser John Bolton testifies at President Trump's impeachment trial, as Democrats want, they have a list of witnesses they would call in return, including former Vice President Joe Biden, his son Hunter, and the whistleblower whose since-verified complaint about Trump's actions with Ukraine sparked the impeachment investigation. Democrats say none of those witnesses are relevant to the charges against Trump, that he withheld military aid to Ukraine to force corrupt investigations of Biden, a top threat to his re-election.

So in Thursday's question period of Trump's impeachment trial, Sen. Amy Kloubuchar (D-Minn.) and Sen. Chris Coons (D-Del.) asked both House prosecutors and Trump's defense team if any of the witnesses Trump's lawyers might call "would have first-hand knowledge of the charges against the president and his actions?" Lead prosecutor Adam Schiff (D-Calif.) said there are "absolutely" such witness, like acting White House Chief of Staff Mick Mulvaney and Secretary of State Mike Pompeo, noting they have both issued statements that seek to exculpate the president.

"Now, the reason they're not on the president's witness list is because if they were truthful under oath, they would incriminate the president," Schiff said. "Otherwise they would be begging to have Mick Mulvaney come testify. ... Why don't they want their own people in? Because their own people will incriminate the president."

Trump lawyer Jay Sekulow said the people Schiff named are Democratic witnesses. He didn't explain why Trump's team doesn't want them to testify, but he did note that Republicans have the votes to call any witness they want without Schiff's permission. "I just think the irony of this," he said, "that we could call anyone we want, except the witnesses we want, but we can call their witnesses that they want."

It looks like the question might end up being moot, because Republicans appear to have the votes to block all witnesses.