Sen. Cory Gardner (R-CO), who had previously been on the fence about allowing additional witnesses in the Senate impeachment trial, said on Wednesday that it was unnecessary to call any more witnesses.

“I do not believe we need to hear from an 18th witness,” Gardner, who faces a tough re-election bid, told Colorado Politics. “I have approached every aspect of this grave constitutional duty with the respect and attention required by law, and have reached this decision after carefully weighing the House managers and defense arguments and closely reviewing the evidence from the House, which included well over 100 hours of testimony from 17 witnesses.”

So far, three Republican senators—Mitt Romney of Utah, Susan Collins of Maine, and Lisa Murkowski of Alaska—have expressed a willingness to call witnesses, which would include former National Security Adviser John Bolton, who reportedly claims in a forthcoming book he heard President Donald Trump detail a Ukrainian quid pro quo. A fourth Republican would give Democrats the 51 votes needed to subpoena documents and call witnesses.