“We think ‘we’re all in this together’ is a better philosophy than ‘you’re on your own.’” Not surprisingly, former president Bill Clinton best summarized the choice Americans face this fall. And now that all the staging, balloons and drone of both conventions are behind us, the choice this November is clear — but so too are the limits of this debate.

Nowhere is the polarization of the parties clearer than on social issues. The Democrats in Charlotte were unabashed cultural warriors, making women’s right to choose, the right to marry whomever you love, immigration reform and an embrace of the Dream Act kids a central theme. And the Republican right turned the platform into a bludgeon in these alley fights. Mitt Romney appeared to be nervously looking for escape routes, but his running mate, Rep. Paul Ryan, has too long an assault record on these issues for him to slip away.

On foreign policy, the neo-cons surrounding Romney terrify even the hawkish “pragmatists” of the Republican Party like Brent Scowcroft or Condi Rice. Led by Vice President Joe Biden, Democrats confidently combined muscle flexing — “Osama bin Laden is dead” — with appeals to Americans tired of endless war. President Obama sought credit for ending the war in Iraq and drawing Afghanistan to a close, promising that the money saved could be used for “nation building” here at home.

On economic policy, Romney, as Clinton phrased it, wants to “double down on trickle down” while Obama pledges to build from the middle class out, without much detail on what that means, other than resisting bad things — blocking deep cuts in key investments like education, opposing efforts to roll back financial reform and Obamacare and promising to not savage Social Security, Medicare and Medicaid. Republicans erected a debt clock to record rising U.S. debt, even as they mocked it by demanding trillions more in tax cuts, largely for the wealthy few.

Romney desperately wants this to be a referendum on Obama’s record, not a choice about future direction. His best case is that the economy is lousy, Obama has failed and we should all “trust Mitt,” as his wife Ann put it. Obama surely benefits if voters focus on the choice. It is simply insulting that Romney has responded to the worst economic crisis since the Great Depression by peddling the same nostrums that Republicans have preached in good times and bad, without changing a comma. And if more of the press corps awakens, Ryan’s choir boy looks will have a hard time selling his budget that would attack programs for the most vulnerable to pay for tax breaks for the wealthy.

What’s notable about the choice, however, is what it excludes. This election features the most polarized ideological choice since Reagan vs. Carter in 1980. Yet issues that are fundamental to the nation’s future are defined out of the debate.

Climate change — growing more catastrophic each passing month — received a passing mention by Obama and mindless denial by Romney. Neither candidate offers any sensible response to the clear and present danger.

The United States can no longer afford to police the world. And Obama’s embrace of extreme presidential prerogatives — even the right to target and kill an American citizen without a warrant, probable cause, much less a trial — threatens fundamental rights. Yet neither issue gets mentioned in this campaign. Neither candidate offers any plan to bring U.S. military spending down to sensible levels.

Extreme inequality now threatens our economy and our democracy, as the money of the rich floods our politics. Romney, of course, is the champion of the one percent. Obama stands boldly for the proposition that billionaires shouldn’t pay lower taxes than their secretaries. Neither proposes progressive tax reforms, changes in CEO compensation policies, increases in the minimum wage or labor law reforms vital to insuring that the rewards of growth are widely shared.

This list could go on. We are headed into a fierce, negative campaign between two candidates representing very different directions and very different Americas. Yet with the nation in deep trouble, the fundamental challenges that must be faced are being ducked.