I'd not been lucky finding any decent analysis until this:

NEWS ANALYSIS Trump’s Risky Bet That the U.S. Can ‘Break the Regime’

By DAVID E. SANGER 31 minutes ago @ NYTimes.com

Mr. Trump’s decision is based on the idea that the U.S. and its allies can force a better deal with Tehran through isolation and sanctions.

does fit with the following from a short while earlier. also at the NYTimes:

Angry and Divided, Iran Fears Deeper Crisis as Deal Ends

By THOMAS ERDBRINK 3:36 PM ET

Iran’s economy was already in free fall. Now the lifeline offered by a deal that was supposed to lift barriers to the West is coming apart, too.

This decision is either part of a strategy or it is not.

Does it change the proxy wars being fought in and near Syria?
Does it open up the possibility of new coalitions with existing allies?
Will Russia take this move to the bank and "help" make it better for their interests and the U.S. can use that relationship to do something in response?
Will pulling out of this deal consolidate the power of those in the EU who have grown weary of all the special relationships with the U.S.? And that somehow empowers the U.S. to do stuff?

If the trump administration does not show something remarkable and unexpected in response to these questions, the decision is stupid. Plain and simple stupid.  Really, really stupid.
Etcetera.

The Europeans don't sound like they will be party to any sanctions.