Historically, that's probably the most likely outcome. NASA has always faced tough political battles for funding all the way back to the middle of the Apollo pr

Historically, that's probably the most likely outcome. NASA has always faced tough political battles for funding all the way back to the middle of the Apollo program and nowhere has that been more apparent than when NASA was trying to replace one major project with another. If you're interested, John Logsdon's After Apollo? Richard Nixon and the American Space Program is a fascinating--albeit depressing--book on the politics of NASA funding. It mainly focuses on Apollo and the transition to STS (and covers some of the alternative paths people at NASA wanted to pursue), but I have no doubt whatsoever that many of the same challenges will plague any ISS replacement, whatever it may be.