Illinois Rep. Mark Steven Kirk, who was a rare Republican vote for a “cap and trade” climate change bill three months ago, says he would oppose the measure as a U.S. senator.

At a Republican rally last weekend in suburban DuPage County, Kirk drew boos from the crowd when he said he voted for the bill “because it was in the narrow interest of my congressional district.”

After pausing to acknowledge the opposition, Kirk drew cheers when he said, “As your representative, representing the entire state of Illinois, I would vote ‘no’ on that bill coming up.”