The Relevance of Hearsay

Republicans have much to say about "hearsay" evidence in the Trump impeachment proceedings.

Here is where they are wrong, and they know it. In a congressional inquiry, hearsay may be used to accumulate circumstantial evidence that can be corroborated and made valid by testimony. The investigators (subsequent prosecutors) can use the information to bracket a target witness to squeeze them to tell the truth. 

If a reluctant witness knows that others heard or saw them, that may compel them to not want to commit perjury. 

That is the case with Ambassador Sondland who at first, failed to tell the truth about his conversations with President Trump. When he realized there were witnesses, he offered to change his story.

This week, Amabassodor Sondlant will testify and offer first-hand evidence that the President was seeking to bribe, coerce, and intimidate the Ukrainian President. That is the subject of impeachment.

President Trump's behavior was corrupt and an example of what the US Policy is trying to correct in the Ukraine and elsewhere. Trump undermined US policy. 

Further, by seeking to withhold weapon systems support to Ukraine, Trump undermined Congress that approved the support. He commingled politics with policy, and undermined national security in the process. That is what impeachment is about.

Republicans who go along with Trump are in violation of their oath of office. 

"In court, such testimony might be barred as “hearsay” — defined as an out-of-court statement that a party offers as evidence to prove the truth of the matter being asserted. Hearsay is generally inadmissible. But hearsay is a rule of evidence, applying only to court proceedings, and even then with so many exceptions that it's often admissible anyway.
First, hearsay is admissible in many government settings, including administrative proceedings, parole hearings, and preliminary hearings in a criminal case; a congressional hearing is not even a court, so it’s not governed by the rule of evidence that makes hearsay inadmissible."
Here's what Yovanovitch said during her October deposition. https://www.nbcnews.com/politics/trump-impeachment-inquiry/live-blog/trump-impeachment-inquiry-live-updates-latest-news-n1065706/ncrd1082511

The Sixth Amendment to the United States Constitution provides that "In all criminal prosecutions, the accused shall enjoy the right ... to be confronted with the witnesses against him"."Hearsay is a statement, other than one made by the declarant while testifying at the trial or hearing, offered in evidence to prove the truth of the matter asserted."[1] Per Federal Rule of Evidence 801(d)(2)(a), a statement made by a defendant is admissible as evidence only if it is inculpatory; exculpatory statements made to an investigator are hearsay and therefore may not be admitted as evidence in court, unless the defendant testifies.[3] When an out-of-court statement offered as evidence contains another out-of-court statement it is called double hearsay, and both layers of hearsay must be found separately admissible.[4]
Hearsay - Wikipedia. https://en.wikipedia.org/wiki/Hearsay