Trump did not "cancel" this meeting. The Iranian delegation said all along they had no intention of meeting with US delegation with weekend. There never was a meeting to cancel - it was just the Trump admin pumping out more market-manipulating propaganda.
Q: Yesterday you told Reuters that 'we're dealing with who is in charge now.' What changed today?
TRUMP: Nothing, it's just that they gave us a paper that should have been better. And interestingly, immediately when I canceled it, within 10 minutes we got a new paper that was much better.