To me, a leader as a President has to have two important qualities. The first is the President needs to have a principled view of what America should be. They have to stand by those principles in the face of opposition. You need an agenda that builds to those principled goals. I think it is important to lead with vision and not act only on focus group information.
The second thing they need is the ability persuade people to follow their vision. They need to be able to build coalitions, pass legislation, and move around obstacles. When people do not agree with your ideas, you have to fine a way to pull them toward you. You need to at least pull the people who are unconvinced.
Reagan was the last President to do both do these things. Reagan really believed that Tax Cuts would be good for the economy, that it was important for America to spend money on defense, and that America has to stand up to the Soviet Union. He did not do these things for political gain or because it would make him popular. He tried to do things he thought would make America a better place. You might disagree with what he did, but you can see there was an agenda there.
I say that Reagan was the last leader to hold the post. I think that George H.W. Bush lacked the ability to communicate his vision to other people. He often looked like he had no vision at all. He lacked the communication skills of a good communicator.
Clinton seemed to leave his principle base. After his defeat on health care he never got his policy feet together again. When he took Dick Morris on as an advisor he seemed to make his policy via polling and focus groups. This made Clinton look like he was just playing politics and not leading.
George W. Bush seems unable to convince people he is doing the right thing. Most of the time he sounds like he is telling people 'if you're not with us, your against us.' This leads people to think he has a go it alone attitude. He does not seem to have the ability to build coalitions. These traits make it harder for him to convince people.
If you liked Reagan's policies or not, a lot can be learned from the way he lead. I wonder if another President will be able to put these skills together again.