A funny thing has happened this election season. While much of the campaign rhetoric has been focused on ObamaCare, the public's focus has now shifted. Entitlements, most notably Medicare, heretofore regarded as the lethal "third rail" of politics, are now being openly debated and have quickly become the defining domestic issue of the next 12 months. 

Mitt Romney's pick of Paul Ryan for the VP slot certainly gave Romney's Medicare proposal, which includes reforming Medicare into a defined contribution system, a large public spotlight. While President Obama incorrectly asserted in last week's debate that Ryan invented this so-called "premium support" approach, this idea has a long bipartisan history of backers including Democrats Dick Gephardt, John Breaux (who proposed premium support with me while in the Senate), Ron Wyden, and Alice Rivlin, and bipartisan Medicare and debt commissions under both Presidents Clinton and Obama. Simply put, Ryan and Romney's latest Medicare proposal already has more bipartisan support in Congress than ObamaCare ever had.

Medicare, and the inherent promise our government gives to its citizens, must be preserved. But to preserve, we must modernize.

This spotlight, along with the growing consensus on the need for entitlement reform, has catapulted Medicare into its surprising slot as the most important domestic issue outside of the economy. According to the Kaiser Family Foundation, in September, 78 percent of Americans rated Medicare as an important factor in deciding whom they will vote for. That's ahead of taxes, foreign policy, immigration, Afghanistan, abortion, and even ObamaCare itself. In 2008, Medicare was the fourth biggest issue on America's mind, and in 2004 it was the fifth. The distinction between the already-passed Affordable Care Act and urgent need for Medicare reform is significant, and voters seem to understand.

This increased attention is deserved. Medicare accounts for roughly $550 billion of spending this year, an astounding 15 percent of all federal outlays — and this number continues to rocket upward. The average American will pay $60,000 in Medicare payroll taxes over his working lifetime; however, he will receive almost $180,000 in Medicare benefits, according to a 2011 Urban Institute study. In the 1950s, one in 10 Americans was 65 or older. By 2030, one in five will be 65 or older. It does not take a health economist to look at these facts and know, without any doubt, that Medicare as currently configured is unsustainable.

And now finally we have a clear contrast between the candidates, laid out in last week's debate. Gov. Romney wants to reform Medicare with premium support, using markets and competition to control future spending. President Obama prefers a more centralized, top-down approach embodied in the Independent Payment Advisory Board, or IPAB.

Medicare will be critical to governing in 2013. Medicare is at the heart of the "fiscal cliff" that looms next year. Medicare funds are tied up in the so-called sequestration that both parties are racing to avoid, and next year calls for an unrealistic 27 percent reduction in doctors' reimbursement. And it is the single largest driver of the increasing national debt over the next 25 years, which is the whole point of both the sequestration, Bowles-Simpson commission, and the reduction in payment rates. 

Medicare, and the inherent promise our government gives to its citizens, must be preserved. But to preserve, we must modernize. It will take a national debate. It will take leadership from our president. It will take ideas from both Democrats and Republicans. But it must be done. And America knows that.

Read more political coverage at The Week's 2012 Election Center.