(CNN) Republican Sen. Cory Gardner of Colorado, who is up for reelection this year, told a home-state news outlet that he does not want additional witnesses to be included in the Senate impeachment trial.

"I do not believe we need to hear from an 18th witness," Gardner told Colorado Politics in a statement published Tuesday. "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."

Gardner's comments are significant given that Democrats hope to flip at least four Republican senators to join them in order to have enough votes to force the trial to include additional witnesses, such as former national security adviser John Bolton or acting White House chief of staff Mick Mulvaney. Without witnesses, the trial could wrap up as early as the end of this week.

For much of the process Gardner has been clear he wouldn't weigh in on his thinking or leanings as he considered the presentations by the House Democratic impeachment managers and the White House counsel. He could be seen throughout the opening stages of the trial taking careful notes during the presentations.

So far, just three GOP senators are seen as having publicly signaled that they would consider voting to include witnesses: Susan Collins of Maine, Mitt Romney of Utah and Lisa Murkowski of Alaska.

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