The entire world's electricity needs could be met via space-based solar power for about 3 trillion; just US for less than the bank bail-outs.
This would green the country for generations, provide a concrete goal for NASA and space privatization, and provide a tangible asset of our era for future generations, as well as restore faith in American ideas, ingenuity, and government's ability to actually build dreams.
This is our generation's 'Hoover Dam' and Moon Landing combined. A *real* moon-shot. Technology is here. Political Will is not.
One could popularize the idea by, say, powering the Washington Monument from the Space Station for a single day.
This is what the America we love, would do in a crisis.