Well, actually, and this is coming from a political scientist who analyzed the middle-east situations. When Bush moved into Iraq and toppled its leadership, there was an unstable element created that allowed ISIS to become a reality. Their goal was to create a radical Islamic state, and that was able to be potentially accomplished with Iraq being so unstable. Plus, a lot of other states in the region had internal uprisings inspired by the fall of Iraq, which created further instability. This allowed ISIS to thrive.
ISIS being destroyed has nothing to do with Trump, but rather coalition efforts for many years alongside ISIS not being stable enough to maintain their huge network. ISIS has yet to be fully destroyed, but their presence is a lot less prevalent. This doesn't change the fact that numerous terrorist networks still exist in the region. So, even if ISIS is gone, the greater overarching threat is not.