U.S. President Donald Trump once boasted about knowing "the best words." Maybe he should have held some back during his phone calls with the leaders of Australia and Mexico — if not for his sake, then at least for his new foreign policy adviser Rex Tillerson.

The U.S. secretary of state survived one of the most contentious Senate confirmations in history on Wednesday, getting through on a 56-43 vote, only to walk into a diplomatic tempest.

In his first week, he'll be dealing with fallout over Trump's severe remarks to Australian Prime Minister Malcolm Turnbull and Mexican President Enrique Peña Nieto, dissent from his own department, a public outcry over a controversial immigration executive order, and escalating tensions with Iran.

"A full plate," as former acting deputy secretary of state Wendy Sherman puts it. "He's going to have to hit the ground running."

Not-so-warm welcome

Tillerson can credit his boss for the tense welcome as he inherits a department in turmoil.

As Tillerson glad-handed his State Department employees for the first time on Thursday, telling his new staff that "personal convictions" should not come at the cost of teamwork, a "dissent channel" cable continued to be circulated among departmental diplomats.

More than 1,000 State Department signatures have expressed opposition to Trump's executive order on immigration, which closed U.S. borders to people from seven Muslim-majority countries, causing chaos at airports and touching off protests worldwide. Some Foreign Service staff resigned over the order.

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U.S. Secretary of State Rex Tillerson delivers remarks to State Department employees in Washington, one day after being sworn in to the new position. (Joshua Roberts/Reuters)

Tillerson has an unenviable job ahead of him, says Sherman, who spent four years at the State Department, mostly as the under secretary of state for political affairs. "It's very tough. I think it will be quite turbulent."

As "unnerving" as the president's actions have been, she says, "Secretary Tillerson is going to have to deal with all of that — and it's quite critical that he do so."

The former ExxonMobil exec will first need a team in place as the new administration continues to lag behind schedule on filling Trump's cabinet. Only six confirmations have gone through, five fewer than Barack Obama had in place by his second week in office.

Sherman notes that Tillerson's deputy hasn't yet been named.

"So not only does he have a big job, but he has to do it [as] the only person in the State Department who has been nominated so far."

Candid calls

What won't help is for the president to begin fraying relations with allies abroad — which is why foreign-policy experts were appalled Wednesday when the Washington Post reported details about Trump sparring with Turnbull over what the president termed a "dumb" refugee deal with Australia.

Trump reportedly told Turnbull that, of the four world leaders the commander-in-chief had spoken with that day, "this was the worst call by far." Reports citing staffers in the room said faces turned "white" as the conversation deteriorated. Trump reportedly bragged about his election victory before the tone turned accusatory, with a flustered Trump declaring Australia's Obama-approved deal to take in refugees would send "the next Boston bombers" to the U.S.

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Former senior State Department official Wendy Sherman says Donald Trump has already set a number of U.S. allies on edge with his tough talk. She suggests incoming Secretary of State Rex Tillerson will have a 'full plate' in the coming months. (Fabrice Coffrini/AFP/Getty Images)

The president hung up after about 25 minutes, cutting short what was expected to be an hour-long congenial conversation with one of America's staunchest allies.

The Associated Press reported that Mexico's Peña Nieto had also shared a tense exchange with Trump, in which the U.S. president warned that he might send national forces south of the border to take care of "bad hombres."

The White House was quick to characterize the talk as lighthearted. "Don't worry about it," Trump told reporters of his "tough" phone calls with foreign allies.

'Hairs on edge'

But diplomats worry.

"The president has set a lot of hairs on edge," Sherman says. "Certainly with the Australians, with the Mexicans, with Europeans."

And those are just friends of the U.S. Trump reserved his most severe warning for Iran, taking to Twitter on Thursday morning to blast off an uppercase threat: "Iran has been formally PUT ON NOTICE for firing a ballistic missile."

It was not the most tactful strategy, says Frank Wisner, a foreign policy adviser who served in the State Department under eight presidents.

"You can't run a Middle East policy without taking Iran into account, without treating the Iranians with some consideration and respect," he says. "Threats aren't going to get you there."

Tillerson's first address Thursday was, for the most part, a boilerplate pep talk. ("Well, my first day is here. I'm on the job," Tillerson said to light laughter. "Hi. I'm the new guy.")

"I encourage all of you to use your natural and well-developed skills to adapt to changes here at home," Tillerson told the crowd.

Misreading the dissent channel

But when Tamara Wittes, senior fellow at the Centre for Middle East Policy at the Brookings Institution, heard the statement acknowledging the post-election tensions and make what seemed to be a reference to the dissent memo, she found the statement to be off-key.

The remark sounded to Wittes like a gross misunderstanding of the dissent channel process, a Vietnam-era mechanism that allows American diplomats to internally register constructive criticism about U.S. policy.

The channel is strictly "about policy, not political differences," she says. By apparently interpreting the cables as an anti-Trump protest rather than opposition to a policy decision, she says Tillerson came off as "patronizing."

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Trump's executive order on immigration, which temporarily closes U.S. borders to people from seven Muslim-majority countries, has set off protests around the world, like this one in Brooklyn. (Stephanie Keith/Reuters)

For his part, Wisner says he believes Tillerson will be a solid secretary of state due to his global negotiating experience as an international oilman, someone who will serve as "a force for good sense, good judgement and mature reflection" in the administration.

He already has the trust of the president, but it's a demanding job, even without the stresses of a workforce dealing with an administration that critics believe to be a major force of global uncertainty.

In the meantime, Wisner says, Tillerson will likely be keen to make his mark rather than stake his reputation on being a diplomatic custodian-in-chief for an unpredictable president.

"He'll want to become part of American history," he says. "I can't imagine he took the job to go around with a broom and a dustpan."