What specifically do you want a leader to do to ensure a 9/11 doesn't happen again?
I don't have a specific answer, but I would hope that our president take the appropriate steps to monitor terrorist networks and their intentions. I am not an expert in these things, but I would hope our president would be. Income equality, climate change and campaign finance are all big and important topics that need addressing but our president will still have to protect our nation. There are those that say Bill Clinton specifically warned Bush about Bin Ladin and Bush didn't take the threat seriously enough. I would hope our president not be naive or myopic in their agenda. I know that as a liberal it's not cool to say that national security is important, but it is.
Well, to ignore the point of your argument here (sorry about that), a sizeable portion of people say Bush was warned about Bin Laden and didn't follow closely enough because it was politically uncomfortable for him with the personal ties his family had to Bin Laden's network. Keeping military and surveillance tabs on his friends was ironically something he avoided before explosively expanding NSA programs to do just that post-9/11.