A myth
Congress has never had the opportunity to consider the full Protocol. In 1997, the U.S. voted unanimously against a single specific protocol relating a waiver of participation for developing nations (July, 1997, S Res. 98). This is the Senate action to which you refer. But the entire treaty hadn't even been completed at the time. It was eventually completed in December, 1997 and then signed by Bill Clinton in November, 1998 and then summarily trashed by George Bush upon his ascendency to office.