NASA wants to increase the crew of the space station beyond the current three, and without such an expansion, meaningful science would be impossible. One problem is the need for another three-man lifeboat, but this can only be bought from Russia. The problem is that the US cannot buy one from a Russian company that sells weapons technology to Iran. It is not entirely clear how a Russian company can prove it is not one of these involved in such sales. It is anybody's guess how much of the US funding given to the Russian space program actually does any good, and how much of it is stolen by Russian bureaucrats.