A leading Republican critique of the House impeachment inquiry is that Democrats are relying on “hearsay” evidence.

The word ‘hearsay’ is bandied about in legal circles all the time, and in its simplest form refers to testimony that quotes what another person said. Hearsay is usually, but not always, inadmissible at a trial. But hearsay rules are complex, and many lawyers say it’s problematic to dismiss the evidence presented during the impeachment inquiry with a hearsay objection.

Two key pieces of evidence have been particularly criticized as unreliable hearsay, or even double hearsay: the initial whistleblower report filed by a member of the intelligence community who was told about President Donald Trump’s July phone call with Ukrainian President Volodymyr Zelenskiy, and diplomat William Taylor’s testimony that a staff member overheard Trump speaking with European Union Ambassador Gordon Sondland about “the investigations” — the day after Trump’s phone call with Zelenskiy.

A look at the use of hearsay evidence in the impeachment investigation:

CONGRESS IS NOT COURT

To begin with, Congress is not a court. It’s a legislative body, and it’s not bound by the centuries of common law that built up around the admissibility of hearsay evidence.

“The rules of evidence don’t apply in Congress. It’s a foolish analysis,” said Edward MacMahon, a criminal defense lawyer from Middleburg, Virginia, who has handled numerous high-profile cases. “The common law rules of evidence were not designed to deal with political hearings.”

David Laufman, who has worked as a federal prosecutor and is now a defense attorney with Wiggin and Dana in Washington, has also worked on Capitol Hill for congressional committees. He said committees are free to set up rules governing testimony as they see fit. He said congressional committees invariably choose to allow hearsay.

“That would be the anomaly if hearsay testimony was barred,” said Laufman.

BUT IS IT RELIABLE EVIDENCE?

Jesse Binnall, a lawyer with expertise in parliamentary proceedings who worked for the Trump campaign in 2016 as its parliamentarian for the nominating convention, readily acknowledged that the rules in a congressional hearing are different from a court. But that, he says, may be beside the point.

“Really I think the argument is not that it’s inadmissible, but that it’s unreliable and of little weight,” Binnall said.

Michael Davis, a law professor at George Mason University who teaches courses on admissible evidence, agreed. He said the hearsay rules have evolved over the centuries for a good reason: to ensure reliable evidence and protect the ability of the accused to cross-examine witnesses.

“I look at it from a trial perspective. None of this would be allowed in court. None of what Congress does would be allowed in court,” Davis said.

HEARSAY IS COMPLICATED

Even if one accepts the argument that Congress should observe the hearsay rules that are used in court, hearsay law is complicated. There are more than 20 exceptions to the general rule barring hearsay.

“You start with the general presumption that hearsay is less reliable. Then there are multiple, multiple exceptions,” Laufman said.

To begin with, hearsay testimony is typically permitted in preliminary hearings and grand jury proceedings, which determine whether a defendant will actually be put on trial.

In a congressional setting, the House impeachment proceedings function much like a preliminary hearing. Ultimately, the House will decide whether to vote on articles of impeachment, the functional equivalent of a grand jury indictment. Those articles of impeachment would then go forward to the Senate for trial.

Another major exception to the ban on hearsay applies to conspiracies: a co-conspirator can offer hearsay testimony about statements made by other conspirators in furtherance of the conspiracy.

Binnall, though, noted that the two major pieces of hearsay that have Republicans agitated — the initial whistleblower report and the testimony of Taylor that his staffers overheard a conversation involving Trump — come from non-conspirators, so those statements would still be banned under a hearsay rule.

As a practical matter, though, Taylor’s hearsay testimony about the conversation between Sondland and Trump gives investigators the opportunity to home in on the participants in the conversation who can testify directly about what was said. Then the question becomes whether those involved in the conversation will actually be willing to testify. Sondland has testified to lawmakers behind closed doors and is scheduled to appear at Wednesday’s hearing.

“If the president doesn’t think a conversation is being accurately related, he could testify himself to what was said,” said criminal defense lawyer MacMahon.