Obama has failed for one simple reason: he is a coward.
The single underlying doctrine holding together the otherwise contradictory coalition known as the Republican party is that low taxes on very rich people and corporations will result in job creation. This doctrine is an utter fiction, which is merely a polite way of saying a damnable lie. All the historic evidence in the United States is against it. Greatest job creation occurs when taxes on rich people and corporations are highest.
Not only is it historically untrue, but also no coherent economic theory posits a universe in which it might be true — although asking coherence of economic theory may be too much.
This, however, has proved to be a a very safe lie. No one, simply no one, ever asks people who are calling the rich job creators to provide any form of support for the notion that letting the rich skate will result in more jobs. The satirists do not ask. James Carville does not ask. The Sunday morning pundits do not ask. No one will challenge this bit of nonsense.
And more to the point: Obama will not.
There is no guarantee, of course, that Obama ever could win another election if he did debate this issue. We will never know because he is a coward.