U.S. President Donald Trump risks diminishing his country鈥檚 international standing if his hostile behaviour towards world leaders continues, but the harm won鈥檛 be permanent, says an expert in global affairs.

鈥淭he good news is that America鈥檚 alliances are very deeply institutionalized. They have a long historical tradition and they鈥檙e very resilient,鈥 said Hal Brands, who holds the Henry A. Kissinger distinguished professor of global affairs at Johns Hopkins University School of Advanced International Studies.

鈥淭he problem is that American allies cannot help but doubt American reliability and credibility at a time when they are frequently being abused or lambasted by the president in the press or in private. And one fears that this might also have an emboldening effect on American adversaries by making them think that perhaps U.S. alliance guarantees aren鈥檛 as iron-clad as they once were.鈥

Reports of tense phone calls this week with Mexican President Enrique Pena Nieto and Australian Prime Minister Malcolm Turnbull, calls that are traditionally amicable chats between a new president and an allied leader, have sparked new fears about Trump鈥檚 ability to stickhandle international relations.

(Officials in both the White House and Mexico's administration disputed reports that the call included a threat to send U.S. troops to Mexico. Turnbull said Friday that he and Trump had a "frank discussion" that ended "courteously," which contradicts news reports that said Trump had hung up on Turnbull.)

Brands says it鈥檚 not unprecedented for American presidents to have difficult relationships with allied leaders. In fact, Richard Nixon spoke in crass and confrontational terms with foreign leaders and Lyndon Johnson had a 鈥渇amously testy relationship鈥 with former Canadian prime minister Lester B. Pearson, he says.

鈥淲hat鈥檚 different in this case is that President Trump has now done this with a series of U.S. allies and partners over the past couple of weeks,鈥 he told CTV鈥檚 Your Morning on Friday. And he鈥檚 seemingly proud of this brash persona he鈥檚 created, while presidents typically pride themselves on being presidential.

But it goes deeper than words. Brands says Trump doesn鈥檛 view allies as any more special than other countries, and that his view is 鈥渋mmoral transnationalism鈥 in that he is just as willing to cut a deal with China or Russia as a traditional ally. He鈥檚 called NATO 鈥渙bsolete,鈥 mused about lifting sanctions on Russia and repeatedly threatened to walk away from trade deals if they aren鈥檛 renegotiated to his liking.

鈥淚t seems to be reflective in Trump鈥檚 case of a long-standing view that American allies and partners are basically freeloaders who are fattening themselves at the American trough. This is something that he鈥檚 repeatedly come back to since the 1980s. So I think the consistency and the level of abuse to which he has subjected American allies and partners is something quite new.鈥

It鈥檚 also having an effect.

U.K. Prime Minister Theresa May is under fire for what critics called her 鈥渘ormalizing鈥 of Trump鈥檚 policies during her state visit last week. A petition demanding an invitation for the president to visit the U.K. be withdrawn, which has been signed by more than 1.8 million people, will be debated in parliament Feb. 20.

Brands says alliances with Canada and the U.K. will endure because they are bigger than any one president but leaders of both countries should worry about a unprecedented level of 鈥渦npredictability鈥 and 鈥渉ostility鈥 from the White House.

鈥淚f President Trump decides that Canada or the United Kingdom has done something that offends him, he may very well lash out publicly as he has repeatedly done before. I think the alliances will survive over the long term but we鈥檙e going to be in for rough sledding.鈥

Beyond his personal relationships with foreign politicians, Brands says Trump is undermining the work of American diplomats and military personnel, who will have to reassure counterparts abroad that America remains committed to its international partnerships.

鈥淭he problem is that they will find themselves continually undercut by tweets coming from the White House, by intemperate statements coming from the president.鈥

Trump is also facing deep division in the department charged with overseeing foreign relations.

More than 1,000 State Department employees have expressed opposition to Trump鈥檚 highly controversial immigration ban on residents of seven Muslim-dominated countries. That follows the resignation of seven senior leaders a few days after Trump鈥檚 inauguration.

Rex Tillerson, former chief executive of ExxonMobil, was confirmed as Secretary of State Wednesday. The 43 Senate votes opposing his appointment was the most in U.S. history for that position.

"You understand that the job of our diplomats and the mission of the State Department is to serve the interests of the United States of America to make our nation safer, our country more prosperous and our country much more secure," the president told Tillerson during his swearing-in.

"I do believe we can achieve peace and stability in these very, very troubled times."

-With files from The Associated Press