This news article describes the current situation as far as the US share in ITER is concerned. In this case, and in the case of ILC, it is the US credibility in upholding what it has agreed to that is the issue.
Sauthoff reiterated Orbach's concern that funding cuts by Congress and other, previous snubs have damaged U.S. credibility as a reliable science partner on the world stage.
Add that to the Alpha Magnetic Spectrometer debacle, and you have the US as an unreliable partner. The US Congress should be proud to take full credit for this.