American policy on Iran

I am not able to understand why Barac Obamas policy on Iran was changed by President Trumps. What prompted him or his govts policy on Iran nuclear deal for change.

In fact, overall policy of U.S. regarding nuclear prolification seems contradictry. Why Pakistan can have nuclear weapons and nuclear program and Iran can not. Why this dual policy? Why Pak needs nuclear weapons?

Why deal with Iran was cancelled? Economic sanctions against Iran are not hurting Iran only. They are creating problems of gap in petroleum products and countries like Saudi Arab are cutting production to create problem .

Why should other countries pay . Isnt it looking like a game to gain profits by hurting other countries economic woos in the name of artificial danger. Is Iran more dangerous than isis.

Why opec countries are gaining profits by cutting production when supply is constrained by imposing sanctions on Iran?

Who wiill win the election?

I want to write but what? What should I write .what are the topics I am interested in? Politics? Certainly. I am interested. For me politics is a tool and means to do good for country and for world. But is our politics doing that? Can we say we are heading in right direction or something more can be done. There is always room for improvement and same is the case for polics. First of all we have to keep in mind that if we are honest and play by rules. Rules which give everyone opportunity for equal chance.

Elections are the time when therr is discussion and people talk about what needs to be done and who is good and who is not.

Can someone predict who is going to win in elections? Pl let me and others know what they think about election outcome and what are your thoughts.