Couple of quick points...
First would be that many dictatorships did not survive the Arab Spring. It would be foolish to think that the government of Saddam Hussein would have survived it. What DID survive the Arab Spring was Iraq's new republican government.
Second, to liberate Iraq and leave the same oppressive government in place, even without the former dictator, makes no sense. You are only changing dictators. It's like leaving the Nazis in charge of Germany.
We did in fact establish and protect a democracy. I was there, I saw it.
One hundred percent of the blame for the current problems in Iraq belong to the withdrawal of American troops. If the US military had a presence, ISIS would never have established a foothold. The Iraqi police and military would have had the top-cover they needed to fight ISIS. However, Obama was more concerned with being the "peace" president than he was in getting it right. That's what happens when you elect someone to be a "first", and you have a President who has been deluded by his role in history.
It takes time for brand new institutions to cement themselves and develop resiliency. Without their trainers the Iraqis lost their initiative and almost half the country. So, going back to the original point, Obamas troop withdrawal paved the way for ISIS success, not Bush.