Conservatives should ask themselves one key question over the remaining months of the presidential campaign: What role should America play in the world?

The answer matters. It will determine whether Americans remain free, prosperous and secure, and whether our nation remains the leader of the free world.

Simple, but true. As Ronald Reagan proved, a president's worldview determines whether he indeed will make the hard choices to defend liberty. In November, voters will have to decide which candidate's vision of America best represents their own.

In America, there are basically two competing visions. One -- based on our history and the ideas and founding principles embodied in our Constitution -- is of a nation that safeguards and advances the cause of liberty. The other is of an America whose leadership always defers to international bodies, including the whims of the United Nations and the European Union.

All Americans should reflect on this: If we do not take up the burden of leadership, who will? And, who would we rather have make decisions over our lives?

If we allow our actions to be determined by other nations that aspire to some evolving idea of "international law" and "international consensus," we should not be surprised by their indifference to our security.

In such a world, the UN could block a raid we want to conduct to destroy a terrorist camp that launched another brutal attack on America. Or our Secretary of State could be hauled up before a European court to answer charges of "war crimes" in Iraq.

The UN or other international body even could decide how Texas, Florida or any other state in the union convicts criminals or manages prisons.

Far-fetched? Right now, liberals in America are working with counterparts in Europe to make these things happen.

If this worldview prevails, our military power would wane. We would quit Iraq and raise a white flag to al-Qaeda. We would attend international conferences with dictators and hope they cut us some slack. We would so tie the hands of U.S. intelligence and law enforcement agencies that they couldn't protect us from terrorist attacks.

If this vision prevails, we would embark on quixotic, hopelessly wasteful campaigns to "provide dignity" to the world's poor -- whatever that means -- as Barack Obama's advisers counsel. We would try to discover others' "values" rather than our own, as Madeleine Albright wants. And we would stick our heads in the sand before terrorists who aim to kill us, believing it would end the "politics of fear" - as liberals malign the strategy of steadfastly defending the lives of Americans.

This vision is, frankly, escapist. It is based on the flawed assumption that America can shed the burden of defending freedom -- the very purpose of our country -- at home and around the world by making easy, painless choices. But such choices would prove fruitless.

If we walk away from Iraq, the Iraqi people will descend into a civil war that could spread throughout the Middle East. Iran may sit with us at an international conference, but it won't forsake nuclear weapons. And if we close Guantanamo Bay, those who cheer will soon fall silent when the terrorists return to the battlefield and resume killing Muslim countrymen as well as Americans.

This will not do. We must assert a better vision for American leadership in the world.

We must restore the influence, respect and strength we saw at the end of Reagan's presidency. We can achieve this with leadership that is as inspiring, visionary and competent as was Reagan's leadership.

First, we must make sure America remains a winner - especially in Iraq and Afghanistan. No one wants to follow a loser. We must do a better job persuading allies we care about their security as much as our own in the long war against terrorism.

Second, we must strengthen our military and reinvigorate our alliances with fellow defenders of liberty. If we aren't militarily strong, diplomacy won't mean a thing.

Third, we must take the lead in reshaping the international system for the 21st century. We need new coalitions and organizations to work around the hard cases when outmoded bodies become locked in battles of self-interest having little to do with freedom.

Finally, we must put our own house in order. America will not remain a great nation unless we rein in entitlement spending before it consumes money for defense and other crucial programs; control our borders to block illegal immigrants, international criminals and terrorists; and reform our educational system to cultivate citizens who truly understand our history and have the confidence in our cause to defend it.

America is a great nation because we first stepped onto the world stage as a defender of liberty. We no more can turn our backs on that historic role, bequeathed to us by destiny, than turn against our Constitution after 221 years.

Still, there is nothing inevitable about America's greatness. For every generation, the fate of our nation lies in hard choices. The critical choice before us now -- deciding the next American president -- will set the course for American leadership for the 21st century.

Kim R. Holmes, Ph.D., is vice president for foreign and defense policy studies at The Heritage Foundation (heritage.org) and author of the new book "Liberty's Best Hope: American Leadership for the 21st Century."