Republican Senate leaders — terrified by the prospect of losing five or more seats in November — have freed their members to vote however they need to vote to get reelected, even if that means bucking the president or the party’s leadership. On at least four votes over the past month — Medicare, housing, the GI Bill and the Farm Bill — Republican leaders haven’t even bothered whipping members to toe the party line or back President Bush’s veto threats. Instead, a GOP leadership aide says leaders have told vulnerable senators that it’s all right to “get well” with voters by siding with Democrats on anything but energy and national security.