It seems that the US under Bush handed the keys to the bus to the International Space Station to the Russians. There were various circumstances that made it seem like a good idea at the time.
Back in 2004, President Bush announced that NASA's aging space shuttle program would be retired in 2010 and — eventually — replaced by a plan to return to the moon. At the time, NASA realized there would be a four-year gap between the space-shuttle retirement and when the new manned space transport system would be in place.
But at that point, it didn't seem like a big problem for NASA to ask Russia to transport US astronauts to and from the space station in the interim. Relations between the two countries were friendly — Bush was telling reporters that he'd looked into Putin's eyes and "got a sense of his soul." What's more, NASA had relied on Russian transport for 29 months after the Columbia disaster in 2003, when the shuttle program was put on hold.
This isn't even the only way that the US spaceflight program is dependent on Russia. The Atlas V rocket — built by a joint Lockheed Martin-Boeing venture and used to launch American military satellites and civilian payloads — runs on a Russian-built engine.
When the Atlas V was being designed in the 1990s, Lockheed Martin got a waiver from the usual Defense Department requirement that critical components be manufactured in the US, partly because the Russian engines were better and less expensive than American options, and partly because of political motivations.
"There was a fear that if we didn't find some way of keeping Russian rocket scientists employed, they would go off and work for Iran or North Korea," says James Lewis, a national security and space analyst.
Anyway, a Peeved Putin is cutting us off - though mostly not immediately. And the subversive Republican US Congress has cut funding for US replacements.