The World According to Donald Trump: The Beginning of the End of the Liberal World Order?

There are known knowns and known unknowns for the U.S. on the global stage -- and some things we don't know we don't know -- as Defense Secretary Donald Rumsfeld famously said in the run-up to the Iraq War 15 years ago. Now another Donald -- who got elected by pledging to rethink America's role in the world and keep friends and foes guessing -- is ushering in an era of unknown unknowns.

"Unpredictability" is the buzzword of Donald Trump's foreign policy lexicon and, not surprisingly, there's a lot we don't know yet about what that means for America and the world in 2017.

That's partly because of factors outside President-elect Trump's control. He inherits a world roiled by problems his predecessors failed to solve -- from North Korea's nuclear ballistic missile ambitions to the deteriorating outlook for Israeli-Palestinian peace; from a war in Syria that's claimed half a million lives to a mutating threat from transnational Islamic terrorism. Meanwhile, an echo across the Atlantic of the forces that carried Trump to power -- populist and nativist backlash against immigration and open borders, a common currency and disruptions caused by global trade -- is sweeping across our closest allies and threatens to splinter the European Union, with Britain's startling vote to exit the EU an oracle of what might be coming.

Aaron David Miller, vice president of the Wilson Center in Washington and a former Middle East peace negotiator for the State Department, sees the foreseeable future as one of crises without solutions -- only outcomes.

The unknown unknowns are fueled by Trump's promise to rip up the playbook of 70 years of bipartisan consensus in Washington that the U.S. is the "indispensable nation," a superpower that, in this view, benevolently deploys economic, humanitarian and military might to promote security and like-minded democracies. Ever since Harry S. Truman invested in rebuilding Japan and Germany after World War II, a theory has guided every U.S. president: that democracies and liberal economies don't go to war with one another. The U.S. saw a self-interest in protecting weaker allies and defending free trade, open seas and rules to promote peace and prosperity.

You wouldn't know it from Trump's campaign rhetoric, but the U.S. spends less than 4 percent of its GDP on defense and foreign affairs. That's half as much as it did at the height of the Cold War, notes Joseph Nye, a former assistant secretary of defense and a professor at Harvard's Kennedy School of Government.

Stephen Walt, a colleague at Harvard, says that as we enter the Trump era, "we are at a moment of probably greater uncertainty than we've been for a long, long time," with many moving parts and huge changes that might occur elsewhere in the world.

In contrast, a quarter-century ago when the Soviet Union was breaking up, many other things held constant, including the U.S. commitment to allies in Europe, Asia and the Middle East, and what seemed then like an inexorable movement across Europe toward political and economic integration.

Today, those currents are in flux. And "the fundamental principles of U.S. foreign policy are up for grabs" under the new president, Walt says.

Candidate Trump flew in the face of foreign policy orthodoxy, questioning the money spent defending European and Asian allies and nation-building in places like Iraq and Afghanistan. The U.S. should never have invaded Iraq, he said, but once there, it should have "taken the oil."

The doctrine Trump dubbed "America First" prompted open letters of alarm from scores of boldface names in the Republican and Democratic foreign policy establishment. It appears to be a narrow and transactional view of U.S. interests, seen through the lens of a business deal. He has implied America will now scratch friends' backs in a fee-for-service model -- and will force adversaries to cut better deals at the lowest price.

[READ: Trump's boardroom diplomacy]

"It's the misapplication of what might be OK in business -- to settle your problems with a couple of other big guys -- that doesn't work in foreign policy," says Stephen Sestanovich, a diplomacy professor at Columbia University and former U.S. ambassador-at-large to the ex-Soviet states.

By calling into question U.S. commitments to defending Japan and South Korea, and rejecting a Pacific free-trade agreement that would have been a bulwark against China imposing its own rules, Trump "has worsened the balance of power he needs to get good results from China. The same is true with (Russian President Vladimir) Putin. If he thinks he can just sit down and come to an accommodation while he blows off our European allies, he's in for a real lesson in geopolitics," Sestanovich says.

Voter sentiment in the U.S. that blamed globalization for manufacturing job losses -- despite all evidence that automation and technology are the bigger culprits -- has given the president-elect what he sees as a mandate to reshuffle the deck on decades of diplomacy, trade and alliances.

Until Inauguration Day, America is left reading Trump's 140-character tweets like tea leaves to foreshadow his policies and whether he meant what he said: forcing Mexico to build a wall and pay for it; branding China a currency manipulator; cooperating with Russia while questioning the value of NATO.

Walt sees "enormous uncertainty over where this could go. He (Trump) can't change everything overnight. You've got a domestic agenda and only 24 hours in the day. You can't get up and fire off a few tweets to end counterterrorism operations in Africa, for example." And globalization, for all the scapegoating by Trump and his base, is unlikely to reverse, Walt predicts.

Constanze Stelzenmüller, a fellow at the Brookings Institution in Washington, sees the backlash to globalization and open borders as an existential threat to the EU: "The big divide is between those who want to be connected with the world and those who think pulling up the drawbridges preserves their prosperity and safety." Tribalism and parochialism -- seen in the rise of anti-immigrant parties in Austria, France, Germany, Italy and the Netherlands - threatens the same European integration that proponents credit for decades of peace and prosperity after World War II.

Euro-skeptic and xenophobic politicians like Geert Wilders in the Netherlands and Marine Le Pen in France are expected to do well in elections this year, and if Le Pen wins, France's retreat would likely strike a death knell for a united Europe. "Even if they don't gain power, the damage they do by destroying discourse, putting liberal democracy on the defensive, and trying to set the agenda is damaging enough," says Stelzenmüller.

So where do the rise of illiberal, anti-globalization forces and Trump's rewriting of the foreign policy rulebook leave America? "With the liberal world order under siege," replies Yascha Mounk, a fellow at the New America Foundation and the German Marshall Fund in Washington.

While it may be a challenge for Trump to turn around the American supertanker of international commitments, Mounk cautions against assuming everything will turn out alright because of bureaucracy and institutions. Trump, after all, gets to choose 4,000 political appointees and there's no reason to believe they won't have influence.

And while U.S. leaders have long been willing to work with autocrats when they saw no alternative to "stability," this is "the first time in living memory that the president of the U.S. is not a defender of the liberal world order and doesn't have a preference for liberal democracies when one is available," Mounk says. He fears Trump won't feel compelled to defend democracies under threat.

Putin may feel emboldened to do whatever he wants in his region, and Xi Jinping could flex his muscles in China's maritime disputes with neighbors if they see Trump tacitly endorsing a tripolar world with distinct spheres of influence. "You may see a more assertive China. They have plenty of cards to play," says Kurt Campbell, a former assistant secretary of State for East Asia.

[READ: A South China Sea of uncertainty.]

It's possible Trump will simply "be blustering and ineffectual, despite making the world a more unstable place and making allies nervous," Mounk says. "But it's also possible this is the beginning of the end of the liberal world order, and the start of constitutional crisis in the U.S. and a crisis of European democracies.

"And there are many possibilities in between those extremes."

Indira Lakshmanan is a Washington, D.C.,-based correspondent and columnist on foreign affairs. She has reported from 80 countries and traveled regularly with Secretaries of State Hillary Clinton and John Kerry. You can follow her on Twitter here.