In the past dozen years Americans have made a major shift in the way they pay for college. Instead of relying on the savings and current income of students, parents and institutions, they have shifted a large share of the burden onto the future earnings of students, creating an ever-growing student loan debt.

That figure, now more than $1 trillion and climbing, poses a serious threat not just to those who owe it, but the overall U.S. economy.

And to stop this unsustainable trend a careful process of review and reform must be instituted, into which political gamesmanship should not intrude.

Unfortunately, though, some Democrats, including President Barack Obama, persist in casting Republicans who offer reasonable - and affordable - proposals on this issue as miserly villains. This is a bipartisan problem that requires a bipartisan solution.

According to the U.S. Department of Education, 71 percent of college students now graduate with debt, now averaging $29,400.

And the student loan system is an administrative nightmare fraught with confusion and waste. Loans are routinely bundled and sold off in ways that obscure ownership, making renegotiation of them difficult.

A study by Goldman Sachs shows that student loan debt has quadrupled in real terms since 2002. A little more than half of the increase is due to higher enrollment and the larger percentage of students receiving education loans.

But at least a quarter of the increase - $250 billion of the debt - is due to higher tuition, room and board fees charged by colleges. Public institutions have led the way in pushing up the cost of college, in large part because state support has not kept up with rising costs.

Thus, in an awful twist, student loans that were supposed to make college more affordable have actually made college more costly.

President Obama has expanded eligibility for a program known as "Pay as You Earn," which tailors monthly student loan repayments to a borrower's discretionary income. It also includes a schedule for eventual forgiveness that is accelerated for teachers and others in public service.

But those changes would help only about 5 million of the 37 million people with outstanding student loans.

The president also has endorsed a student loan reform bill proposed by Sen. Elizabeth Warren, D-Mass.

However, that bill contains a poison-pill tax increase opposed by Republicans.

And as Sen. Marco Rubio, R-Fla., and Rep. Tom Petri, R-Wis., recently wrote in an op-ed on the CNBC website, Washington must do more than simply expand student loan forgiveness "while doing little to address the confusing bureaucracy that causes so many borrowers to fall through the cracks."

They warned: "This approach is fundamentally wrong and will only reward over-borrowing while leaving taxpayers holding the bag. Instead, young workers need a streamlined and dynamic repayment system that automatically adjusts to their ability to pay over time. This would protect them from the financial ruin of default but in a way that is fiscally sustainable, fair and that encourages prudent borrowing."

Clearly, both parties must find a practical middle ground for changes that balance incentives for student loan repayment by those who can afford it and effectively targeted forgiveness for those who can't.

Just as clearly, playing politics with this issue won't resolve it.