The most important geopolitical fact of our time is the relative decline of the United States.

A generation ago, at the conclusion of the Cold War, pundits spoke convincingly about a "unipolar moment," with the U.S. standing astride the globe, far surpassing every ally, rival, and opponent in the world both economically and militarily. But that moment has passed. China has become a formidable world power with grand economic and military ambitions. India is close behind. Russia projects power to its near abroad, threatening conflict with NATO, and in the Middle East. Brazil hopes to become a regional powerhouse in Latin America and possibly beyond. All of which means that a new multipolar era has arrived.

Not that you'd know that from listening to speeches of elected officials in Washington or reading policy statements released by the Pentagon and the leading think tanks of the foreign policy establishment. All of them continue to think and talk as if American primacy — our ambition to be indisputably the most powerful nation in the world — remains a present reality and realistic future prospect.

It is neither — and the failure to confront this fact and think through its implications for the country and the world runs the significant risk of inviting geopolitical disaster.

This isn't to say that no one in Washington has woken up to the reality of America's relative decline and the need to rethink the ideology of primacy that dominates the nation's capital. A number of new, promising initiatives have opened up space for debate and discussion around these issues, including preliminary efforts to rethink American grand strategy in a multipolar world.

Yet so far such debate and discussion has remained very much on the margins, with critics of the prevailing consensus mainly engaging in counterpunching against reflexive military interventionism and sloganeering about the need to "end endless wars." Much of that is welcome. The liberal internationalists, neoconservatives, and hawkish realists who dominate foreign policy conversation in Washington should be challenged and forced to defend their policy preferences against tougher critics than they've confronted in recent decades. But much more still needs to be said and done.

The United States undergirds its ambition to primacy through tripwire policies around the globe. Ever since the articulation of the Monroe Doctrine, the U.S. has threatened to respond militarily to meddling by foreign powers in our hemisphere. NATO commits us to defending Europe from threat or invasion, most likely from Russia, so we maintain tripwires across the continent's eastern borders. Multiple American tripwires ring the Middle East, protecting Israel, Saudi Arabia, and the Kurds from various threats, monitoring the remnants of ISIS and other terrorist groups, and deterring Iran. Our continued presence in Afghanistan serves as a tripwire against the Taliban once again taking over the country. A formal tripwire on the Korean peninsula has kept the peace for 67 years, just as an informal one in the South China Sea protects Taiwan from China.

These tripwires constrain the actions of rising powers. As those powers grow stronger, they will be tempted by national interest and honor to test them to see if we are bluffing. Are we really willing to fight wars to defend the territorial integrity of countries in Latin America, Eastern Europe, the Greater Middle East, and Asia? And even if we are, what if two rising powers called our bluff at the same time — with, say, China launching an offensive against Taiwan while Russia moves against Ukraine or one of the Baltic states? Even the most hawkish foreign policy strategists concede that we probably aren't capable of waging two significant wars simultaneously. Yet we are committed to doing exactly that if two wires get tripped in quick succession.

This would leave us facing a terrible choice between honoring our security guarantees by entering into one or more potentially ruinous wars or backing away from them in the face of a direct challenge, which would have the effect of making the U.S. look like a paper tiger and of inviting additional challenges in other regions.

Considerations like these have led me to favor the U.S. withdrawing troops from Afghanistan and to oppose the U.S getting even more deeply involved in Syria, Libya, Yemen, and Venezuela. This implies that I think the tripwires the U.S. has already laid in these places should be removed and the attendant security guarantees withdrawn. Many critics of the still-regnant foreign policy consensus in favor of American primacy have made similar arguments for the U.S. pulling back from these and other regions of the world.

What most of these critics have failed to do — and I very much include myself in this rebuke — is make explicit the grand strategy assumed by these policy proposals.

One possibility is that such proposals for withdrawal follow from a broader commitment to the U.S. pulling out from most or all of our security guarantees around the world — in Asia, in the Middle East, in Europe — on the rationale that either we should never have extended them in the first place or the context that once justified them (the Cold War) is no longer present. The trouble with such reasoning is of course that once such promises have been made, pulling back from them cannot help but be seen as evidence of weakness, giving geopolitical rivals and opponents a proverbial green light to do whatever they want everywhere without fear of American reprisals and without consideration of American interests.

Presumably very few critics of U.S. foreign policy would favor such a drastic shift in the direction of outright isolationism. (That term of abuse is usually hurled indiscriminately and unfairly by hawks at anyone who dares to question the interventionist consensus. But in this case, it would be apt.)

That leaves any number of less extreme adjustments to a multipolar world. But what should they be? Former President Barrack Obama attempted one — a pivot to Asia to hem in China paired with openings to Iran and Cuba and a partial pullback from our multiple theaters of military involvement in the Greater Middle East. (I supported most of this agenda during the Obama administration and continue to think it was an intelligent response to present realities.) Trump has shredded all of that, of course, replacing it with an incoherent mishmash of primacist muscle flexing, deference to dictators, hostility to allies, and rhetorical gestures toward bringing troops home that have thus far come to nothing.

If Joe Biden wins in November, he will face a daunting decision about whether to try reverting to Obama's list of priorities — or to devise a different set. There are many possibilities. One would be to focus on our hemisphere and Europe, ceding Asia to China but attempting to check its ambitions in Africa. (I'm partial to that alternative.) Another would be to double down on Latin America and Asia, risking war with China, while pulling back from our commitments to Europe. There are of course other options.

What is not an option is continuing to defer such rethinking of the geopolitical order. Burying our head in the sand and pretending we're still king of the world simply isn't a serious response to the situation in which we find ourselves.