Donald Trump will set aside his bad-boy antics, and with the help of a teleprompter to keep him on message, outline on Wednesday his vision for foreign policy if elected U.S. president in November, campaign aides say.

Governments alarmed at the prospect of a Trump presidency will be paying close attention. Critics have accused the Republican front-runner of bigotry and posing a danger to U.S. national security.

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Many foreign policy and defense advisers say his views are worrying, mingling isolationism and protectionism, with calls to force U.S. allies to pay more for their defense and proposals to impose punitive tariffs on some imported goods.

"Part of what I'm saying is we love our country and we love our allies, but our allies can no longer be taking advantage of this country," Trump told reporters on Tuesday night in a speech preview.

He said he would focus on nuclear weapons as the single biggest threat in the world today.

The billionaire businessman, 69, promises to temporarily ban Muslims from entering the United States and to build a wall to block off Mexico.

His policies are popular with many voters who want a change of viewpoint in Washington, but foreign policy elites are concerned.

“It’s a perfect storm of isolationism, muscular nationalism, with a dash of pragmatism and realism," said Aaron David Miller, a foreign policy scholar who has served in Republican and Democratic administrations.

The speech, at noon at a Washington hotel, will address several critical foreign policy issues including global trade and economic and national security policies and building up the U.S. military, his campaign said.

It is expected to be the first in a series of policy speeches meant to show that Trump, fresh off a sweep of five Northeastern state nominating contests on Tuesday, is worthy of the White House despite having never held public office.

"He needs to show that he has the substance, the depth of knowledge and the vision to be the American commander in chief," said Steve Schmidt, who was 2008 Republican nominee John McCain's campaign manager.

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Trump's biggest backer in Washington, Republican U.S. Senator Jeff Sessions, said Trump would offer "a more restrained foreign policy, a more realistic foreign policy that counts the cost not only now but in the months and years to come."

Driving much of Trump's rhetoric is what he feels is the need to ease the U.S. financial burden overseas, focus more on nation-building at home and make sure American companies pay a price for outsourcing jobs to countries where labor is cheaper.

"His views are reckless and dangerous but that doesn't necessarily mean that they’re unpopular. That's part of the challenge," said Lanhee Chen, who advised former 2016 Republican candidate Marco Rubio and 2012 Republican nominee Mitt Romney.

Trump has declared NATO obsolete and said European countries should be pulling more of their weight in the post-World War Two alliance. Democratic President Barack Obama has for years urged Europeans to bolster their defense spending to help NATO, but unlike Trump has never said the alliance needs to be reconfigured.

In a joint paper published this month, national security and regional experts at the Center for Strategic and International Studies rejected Trump’s position on overseas bases.

“The United States gets the better end of the deal from its forward deterrent posture than any other nation, and its value outweighs its current costs,” Kathleen Hicks, Michael Green and Heather Conley wrote in Foreign Policy magazine.

Trump says South Korea and Japan are too reliant on the U.S. military presence there and should be paying for it, and that they might need to develop nuclear programs to counter North Korea's atomic belligerence – a statement that prompted Obama to say Trump was ill-informed on international relations.

Former U.S. Navy chief Admiral Jonathan Greenert, a former commander of the Japan-based U.S. Seventh Fleet, said it was not accurate to suggest Japan and South Korea get a free ride from the United States, since both countries are subsidizing their U.S. base presence by billions of dollars a year each.

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In the Middle East, Trump has said he would use U.S. forces to "knock the hell out of ISIS" and get the forces out quickly, and create safe havens for Syrian refugees so they do not come to the United States.

Dennis Ross, who served as a Middle East adviser to both Democratic and Republican administrations, said Trump’s rhetoric suggested his worldview was something of a throwback to political thinking that drew a significant following among Americans before the U.S. entry into World War II.

"I don’t think that anyone would feel they could count on the United States,” Ross said.