Bush broke the ABM treaty with ease.
Yes, but that was a calculated move and was actually within the terms of the treaty. Technically he did not "break" it.
Treaties are the law of the land (Article VI Clause 2) and actually breaking them without the support of Congress is an impeachable offense. A nation does not back out of a treaty without a careful calculation of the consequences. That doesn't mean it is never done, just that it is not done lightly.
The fact that one of the signatories ceased to exist(Soviet Union) meant the the treaty no longer did either. That's not the case here.