A Trump presidency thus promises a fundamental realignment of America's relationship with the rest of the world and a scrambling of decades-old military alliances, international institutions and foreign policy priorities in an era of rising global instability.
It is unclear if Trump will choose advisors who will advocate a more conventional approach. Names the Trump campaign has circulated as possible Cabinet members so far do not include noted diplomats, experts or other successful veterans of foreign policy.
Trump offered mostly vague and contradictory national security nostrums during the campaign. In April, in his only foreign policy speech, he promised to be "reliable" and "unpredictable" on the world stage.
Skeptics at home and around the globe now worry that control of America's nuclear arsenal is about to go to someone with no experience in governing or in military and international affairs.
Trump sought to calm those fears in his victory speech early Wednesday morning, saying he expects to have "great, great relationships" with other countries.
"I want to tell the world community that while we will always put America's interests first, we will deal fairly with everyone, with everyone — all people and all other nations," he said. "We will seek common ground, not hostility, partnership, not conflict."
Those conciliatory comments, analysts were quick to note, appeared in conflict with the provocative positions Trump struck during the long, ugly and hard-fought campaign.
Trump turned 70 years of American foreign policy under both Democratic and Republican administrations "on its head" during the campaign, R. Nicholas Burns, a former senior State Department official who now teaches at Harvard, wrote in an essay Wednesday.
He “consistently denigrated”
He should "signal quickly and unequivocally that he intends to be a faithful ally and to protect these countries from Russian and Chinese aggression" in Eastern Europe and the western Pacific, Burns added.
Trump's criticism of NATO "deeply rattled the Baltic states, Poland and other former Warsaw pact nations," said James Stavridis, the retired U.S. admiral who served as NATO chief until 2013 and is now dean of the Fletcher School of international affairs at Tufts University. "I hope the new administration will give NATO a chance to prove its value to the United States… but it will certainly be a skeptical appraisal."
During the campaign, Trump vowed to dismantle the NAFTA and CAFTA free trade agreements and to kill the proposed Trans-Pacific Partnership trade deal, which
He also pledged to withdraw from the historic Paris climate change agreement, which was signed by 193 nations in December in an effort to reduce greenhouse gases and cool the warming planet.
His lavish praise for Russia's president seemed the most mystifying to the U.S. foreign policy establishment.
"The biggest single Trump turnabout will likely be relations with Russia," said Cliff Kupchan, chairman of the U.S.-based Eurasia Group risk-analysis organization. "He's an outspoken admirer of President Vladimir Putin, and the feeling's mutual."
During the campaign, Trump called Putin a "strong leader," better than the U.S. president, and refused to condemn Russia's military interventions in Ukraine and Syria. He suggested he may not defend NATO allies if Russia pushes into Eastern Europe.
Trump also said he wants to strike alliances with Putin, especially in the fight against Islamic State. U.S. experts say Russia’s military is not targeting the terrorist group in Syria, but is fighting to defend Syria’s dictator,
Most U.S. experts and diplomats view Putin as a belligerent and autocratic Russian nationalist who increasingly challenges and undermines U.S. interests.
During the campaign, the director of national intelligence said senior Russian officials had directed the hacks of thousands of emails from Democrats. Trump benefited from the leaks and is not likely to approve retaliation, experts say.
With Republicans in control of Congress, Trump is likely to have a free hand in issues the GOP opposes, like the climate change deal and the landmark Iranian nuclear deal.
Republican lawmakers also will support Trump's vow to keep open the Guantanamo Bay prison in Cuba and to expand its use. Since 2009, they have blocked Obama from closing the controversial facility.
Whether they would also endorse Trump's call to torture terrorism suspects and to kill their families is less clear.
But Republicans generally still believe in a robust NATO and are less conciliatory toward Russia. That could be a mitigating force as Trump learns foreign policy on the fly.
Trump must "find the right balance between reassuring an uncertain world… while avoiding commitments that exceed the tolerance of the American public," said Bruce Jones, a senior fellow at the nonpartisan Brookings Institution think tank.
Trump gave mixed signals on his intentions on the war in Syria, alternately suggesting a more muscular response and vowing not to get involved. He showed no interest in the humanitarian crisis there, saying his only focus is on fighting Islamic State.
That could prove decisive in the country's bitter civil war, where U.S. backed rebels have struggled to hold ground against Russian, Iranian and Syrian government forces.
"The only thing holding up the moderate rebels in Syria after six years of war is the United States," said Christopher Harmer, a military analyst at the Institute for the Study of War, a public policy group. "If the Trump administration falters in that support, the moderate rebellion in Syria is over. Full-stop."
Trump also gave mixed signals on his plans for the U.S. military. He vowed to boost defense spending to expand the Army and to build more ships, warplanes and arms, but also pledged to avoid more foreign wars like those in Iraq and Afghanistan.
"If we're going to sit back in our fortress with two oceans on either side of us, what do we need more weapons for?" Harmer asked. "Guess we'll find out. "
Mackenzie Eaglen, a defense analyst at the American Enterprise Institute, said Trump's foreign policy is likely to be less radical than his inflammatory language suggested during the campaign.
"My experience has been that once new presidents start getting daily briefs and see how scary the world is, reality sets in, and they re-think their stances," she said. "I'm confident he'll reassess his assumptions."
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