If the U.S. reneges on agreements, what/who can be trusted?

U.S. Won't Honor Previous Understandings with Israel - Barak Ravid
Israeli political officials expressed disappointment after last week's round of meetings in London with George Mitchell, President Obama's envoy to the Middle East. "All of the understandings reached during the [George W.] Bush administration are worth nothing," said one senior official....Brig. Gen. Mike Herzog spoke to Mitchell and his staff about understandings reached by former prime ministers Ehud Olmert and Ariel Sharon with the Bush administration on allowing continued building in the large West Bank settlement blocs...The Israelis were stunned by the uncompromising U.S. stance, and by statements from Mitchell and his staff that agreements reached with the Bush administration were unacceptable.
..."the Americans took something that had been agreed on for many years and just stopped everything." The Israeli envoys said the demand for a total settlement freeze was not only unworkable, but would not receive Israel Supreme Court sanction(Ha'aretz)