Mandatory service at the age of 18 for US citizens. There would be the choice to go into the military or community service. Less appealing choices would offer extra benefits (extra pay, professional training/certification, etc).
Community development service would be paid and may only take up a few hours per week. Service would offer a way to develop under served aspects of American communities, create jobs, and establish an economic and social base in economically stagnant communities.
Mandatory Service represents a chance for America to invest in itself, create jobs, and offer invaluable experience.