2. USA backs a candidate and initially gets a government elected that is favorable to the USA. However, these politicians turn out to be kind of scummy and screw up just about everything.
3. Iran realizes that elections can be influenced (they watched the USA influence the first election), and having lots of paramilitary type forces that are trained in information operations, decides to capitalize. They flood across the porous border to spread propaganda (the current scumbags in government make it so the Iranian propaganda doesn't even have to lie, it just has to point out how much the current guys suck).
4. Iraqi citizens, growing sick of the crappy politicians they elected initially, start listening to the propaganda and elect a government friendly to Iran. This is the first time this has happened in a long time, Iraq has not been allies with Iran for several decades.
5. End result- USA invades, eventually loses influence to Iran. The global hegemony USA got outplayed by a regional hegemony because they backed unethical and incompetent sellouts rather than finding a good candidate.