The federal student loan program seemed like a great idea back in 1965: Borrow to go to college now, pay it back later when you have a job. But many borrowers these days are close to flunking out, tripped up by painful real-life lessons in math and economics. Surging above $1 trillion, US student loan debt has surpassed credit card and auto loan debt. This debt explosion jeopardizes the fragile recovery, increases the burden on taxpayers and possibly sets the stage for a new economic crisis.