WASHINGTON (NEXSTAR) — Democrats are still pushing for President Donald Trump’s former National Security Adviser John Bolton to testify in the Senate impeachment trial.

“No trial will be a fair trial without witnesses and documents and John Bolton is a key witness,” Senate Minority Leader Chuck Schumer, D-New York, said.

Senator Bob Casey, D-Pennsylvania, believes Bolton may have first-hand knowledge that could shed light on critical moments in which aid to Ukraine was being held up for political dirt on Trump’s political rivals.

“We’re not asking for them to come in and testify about something that is extraneous and irrelevant. We’re talking about relevant information,” Casey said. “I don’t know if John Bolton has evidence that is exculpatory for the president, in other words, that benefits the president, we don’t know that.”

Regardless, Senate Majority Leader Mitch McConnell, R-Kentucky, said he has the votes to proceed with the Senate impeachment trial without calling new witnesses.

Bolton said previously he would testify if he was subpoenaed by the Senate, but Trump said he would, in turn, invoke executive privilege to block such testimony from happening.

“He would know nothing about what we’re talking about,” Trump said.

But Schumer said if Bolton is subpoenaed, Trump’s executive privilege won’t stop him from testifying.

Even some Republicans, like Senator Mitt Romney, R-Utah, support hearing Bolton testify.

“The Clinton impeachment process allowed for witnesses to be determined after the opening arguments, I’m comfortable with that process,” Romney said.