Former Sen. John Warner (R-Va.) has warned of “the lasting damage” that could be done to the Senate and the country should Republicans block witnesses from testifying in the impeachment trial of President Donald Trump.

Warner, in a Thursday statement on the eve of the Senate’s vote on witnesses, said that “as conscientious citizens from all walks of life are trying their best to understand the complex impeachment issues now being deliberated in the U.S. Senate, the rules of evidence are central to the matter.”

NEW: Former Senator John Warner, a Republican and elder statesman of Virginia politics, has issued a statement calling on fellow Republicans to follow “judicial norms” by “welcoming relevant witnesses and documents” in President Trump’s impeachment trial. pic.twitter.com/GeRRjIkHfo — Sheryl Gay Stolberg (@SherylNYT) January 31, 2020

Warner, who retired in 2009 after serving 30 years in the Senate, argued the chamber was also on trial and “as such, I am strongly supportive of the efforts of my former Republican Senate colleagues who are considering that the Senate accept the introduction of additional evidence that they deem relevant.”

“If witnesses are suppressed in this trial and a majority of Americans are left believing the trial was a sham, I can only imagine the lasting damage done to the Senate, and to our fragile national consensus,” he added.

He continued:

I respectfully urge the Senate to be guided by the rules of evidence and follow our nation’s judicial norms, precedents and institutions to uphold the Constitution and the rule of law by welcoming relevant witnesses and documents as part of this impeachment trial.

Democrats need four Republicans to side with them to allow witnesses,

However, Sen. Lamar Alexander (R-Tenn.) on Thursday said he will vote with the GOP to block witnesses, suggesting Democrats’ bid for a fair trial will fail.