Will a three-party system work in the US?

Political analysts pretty much agree that, with the selection of Palin as his running mate, McCain’s legacy will be that of catalyst to the rending of the Republican party in two. Civil war within the Republican party appears inevitable. The factions appear to line up as Republicans and a new conservative populist party. While there have always been multiple parties within American politics, in general third parties do not have the membership or financial clout to be electable on a national level. Their role has been to shape platform and policies of the major parties. How will a split in the Republicans change American government?