Whether a country is democratic or not doesn’t really have anything to do with it. Every country, including non-democratic ones, has different factions and inner workings.
We cannot blame a single president for the same
Is this a typo? You just said that Trump was responsible for pulling out of the Iran deal, which is true, and which he had the power to do unilaterally.
That’s not true. Even in dictatorships, the person at the top still has people who they need to keep happy in order to stay in power. Nobody gets to or stays at the top on their own, what happens is that they’re supported in that position by whatever interests they represent. If someone comes to power in a military coup, for instance, they have to keep the military happy or they’ll get replaced.
More to the point, it’s not just about who gets blame or credit for stuff, it’s about understanding the mechanics of a system, and the history, and the various material factors and interests that go into decision making.