But instead of a landmark debate, Republicans found themselves filibustering their own amendment to stop it from coming to the floor on Wednesday for a straight up-or-down vote -- out of fear that it might fail to get even 51 votes, much less the 67, or two-thirds majority, required to amend the Constitution. Republicans apparently were taken by surprise when Democrats, sensing a huge victory, offered to lift their own objections and proceed to direct consideration of the measure.