"It is rattling the windows of foreign ministries all over the world," said CNN's senior political analyst David Gergen, who has worked for a string of Democratic and Republican presidents.
Trump has gone to great lengths over the past week to explain his foreign policy views, which are often criticized as overly vague. He's participated in extensive interviews with The Washington Post
and The New York Times
and delivered a speech -- notable because it was carefully pre-written -- to the leading pro-Israel group in Washington. He'll have another opportunity to address foreign policy Tuesday night during a CNN town hall in Milwaukee, Wisconsin.
The interviews reveal Trump as someone who is just as willing to flout the foreign policy establishment as he is the GOP elite. His statements appear to fly in the face of the longstanding assumption underlying U.S. foreign policy -- that supporting allies financially, diplomatically and militarily promotes a global system of unfettered free trade, democracy and stability that is overwhelmingly in the national interests of the United States.
Return on investment
Instead, Trump views America's allies more as a global tycoon might judge a foreign venture: in terms of a return on investment. And in many instances, he seems to think the price the U.S. pays to keep order abroad is way out of whack.
"We have been disrespected, mocked and ripped off for many years by people that were smarter, shrewder, tougher. We were the big bully, but we were not smartly led," Trump told The New York Times.
Trump's world view -- requiring allies like those in Europe and Asia to pay a higher price for security protection -- is also rooted deep in a sense of American decline, ingrained in his campaign's philosophy that he will "Make America Great Again."
"We're a poor nation, debtor nation," Trump told the Times, adding that America's nuclear arsenals were "in a terrible shape," its military was "severely depleted" and that the nation is "obsolete" in cyber warfare.
Trump's businessman's eye seems to pay less attention to the economic consequences that could flow from a sharply different U.S. global posture.
Those include the oil price shocks that could result in a U.S. downgrading of its security role in the Gulf, or a trade war with China over its alleged currency manipulation.
Establishment critiques of his foreign policy are unlikely to have much clout with the grass-roots Republican voters who have flocked to Trump's campaign. But they could play into a general election if Trump becomes the GOP nominee as all presidents must convince voters that they can pass the "commander-In-chief" test and can be trusted to lead America in a treacherous world.
His ideas would contrast dramatically with those of former Secretary of State Hillary Clinton
, who is billing herself as the only candidate qualified to keep America safe on day one in the Oval Office.
Losing patience with the establishment
And though his view may resonate with his faithful supporters who have lost patience with establishment politicians and their establishment solutions, Trump's Republican rivals sense vulnerability, seeking to turn his inexperience in foreign affairs into a liability at a time when many members of the GOP foreign policy community are quietly voicing alarm at his policies.
Texas Sen. Ted Cruz
, for instance, has accused Trump of wanting to pull out of NATO
and says his policies are tantamount to a dangerous form of isolationism.
Trump responds that he does not in fact want to exit the Western alliance but seeks a fairer division of the costs of NATO with U.S. partners. He says the group does not do enough to fight terrorism.
Trump's views have also caused consternation and criticism in Washington's national security establishment
-- a factor the billionaire would probably regard as a badge of honor for his outsider presidential campaign.
"There's no premium in his thinking on coherence so far as I can tell," said Daniel Serwer, a senior research professor at the Johns Hopkins School of Advanced International Studies.
Serwer pointed to Trump's positions on Israel
and on resolving its decades-long conflict with the Palestinians. On the one hand, Trump said he would take a neutral position on Mideast peace, on the other "he has suggested moving the U.S. embassy to Jerusalem, which ends any pretense of neutrality," Serwer said.
Republican political consultant Kevin Madden said on CNN's "The Situation Room with Wolf Blitzer" on Monday that Trump was playing into a palpable sense among some Americans that they did not feel as safe as they should.
But he added: "I think where Trump skeptics and Trump critics are right is that he doesn't offer a whole lot in the way of details and also he doesn't offer a whole lot in the way of reality."
Trump's plan to reshape American foreign policy is perhaps most striking on nuclear policy.
He told the Times that "the biggest problem, to me, in the world, is nuclear and proliferation." That said, he also opens the possibility that non-nuclear nations such as South Korea and Japan could develop their own weapons programs as a way of alleviating the global burden on the United States.
"It's a position we have to talk about," Trump said.
Bruce Blair, a nuclear expert with Princeton's Woodrow Wilson School of Public and International Affairs, said Trump's stance is "off the cuff, like everything else he does, instinctive, with no thought about how these things would play out."
Trump displays some historical amnesia on nuclear weapons, overlooking the U.S. use of atomic bombs in Japan at the close of World War II when he told interviewers that being the first nation to use them would be "a very bad thing."
Trump's foreign policy blitz comes with the GOP front-runner under increasing pressure from his opponents to lay out some of his foreign policy ideas. He first caused shockwaves with his critique of NATO in a Washington Post editorial board interview last week.
He raised the prospect of diminished American involvement in the Western alliance.
"We certainly can't afford to do this anymore," Trump told the Post. He later said, "NATO is costing us a fortune, and yes, we're protecting Europe with NATO, but we're spending a lot of money."
In one sense, Trump is playing into existing and longstanding irritation in Washington at the reluctance of some NATO allies to pay their way amid shrinking defense budgets brought on by Europe's economic crisis. Some European countries have struggled to reach the alliance's requirement that 2% of GDP be devoted to defense spending.
President Barack Obama recently told Atlantic journalist Jeffery Goldberg that "free riders aggravate me" and successive administrations have chafed at transatlantic allies.
But judging NATO in purely financial terms, some Trump critics argue, does not take into account the success of an alliance credited with ending Europe's heritage of bloody wars between its major powers that remains a prominent instrument in the projection of American power around the world.
"It holds the United States and Europe together and that is the crucial anchor point for world affairs today," said former NATO Supreme Allied Commander Wesley Clark, who supports Hillary Clinton's Democratic campaign, on CNN's "New Day" on Monday. "Yes, we can always talk about strengthening NATO and we can always talk about European nations contributing more to their own defense .... we don't want to let go of that linkage with Europe. It is vital for America's national security. it's for our benefit, not Europe's."
Departure from decades of policy
One of the reasons Trump's intervention may be so alarming to America's allies is that it appears to be a departure from decades of American foreign policy pursued by presidents of either party.
He's not, for example, an internationalist like former President George H.W. Bush, who believed the world needs global cooperation. Nor does Trump seem in the mold of the second President Bush, who advocated regime change and democratization in the Middle East.
And he does not seem to be a hard-nosed preacher of realism in statecraft like former secretary of state Henry Kissinger either, and his willingness to countenance the use of force against groups like ISIS appears to rule out the idea that he is a classic isolationist.
"We won't be isolationists -- I don't want to go there because I don't believe in that," Trump told the Times. "But we are not going to be ripped off anymore by all of these countries."