"Mad Dog," the nickname James Mattis earned for his battle toughness and the many blunt statements attributed to the retired general, may have endeared him to a president-elect who is himself not shy to speak his mind.

But the moniker bestowed on Mattis belies the fact that Donald Trump's Pentagon pick is a true intellectual well versed in history and politics, said Xenia Wickett, head of the US and Americas program at British think tank Chatham House, who has met him personally.

"He has enormous experience not just in the military, but foreign policy more broadly," she said. "He has effectively been a diplomat as well as a military officer.”

Tough and intelligent

John Harper, who studies American Foreign Policy at Johns Hopkins University's School of Advanced International Studies in Bologna, Italy, was less enthusiastic about Mattis.

"Given Trump's views, he could have picked a worse choice," Harper said. "My impression of Mattis is not negative. I don't think he is a loose canon and I don't think he is a lunatic. He seems tough, but intelligent and fairly stable.”

More important than his qualifications for the job, which he clearly possesses Wickett and Harper agreed, is what his appointment says about a possible Trump foreign policy and how he fits into the president-elect's cabinet, which is now beginning to take shape.   

But the still blurry sketch of what might the Trump administration's foreign policy will look like has not been made any clearer by Mattis' nomination.

Key differences

First, Trump and Mattis have differences on a range of key issues including Europe, the Israeli-Palestinian conflict and Russia. Unlike Trump, Mattis, who has served in a leading role in NATO, appreciates the role of the transatlantic military alliance and America's European partners. Unlike Trump, Mattis supports a two-state for Israelis and Palestinians and has been critical of Israeli settlements. And unlike Trump, Mattis is deeply skeptical about Russia's international role and has warned that Moscow aims "to break NATO apart."

But it is not only the apparent contradictions between Trump's and Mattis' stances that make it difficult to presume what direction the new administration's foreign policy might take. The eclectic nature of Trump's personnel choices, symbolized best by his selection for National Security Advisor, Michael Flynn, coupled with the president-elect's utter lack of foreign policy background still has observers scratching their heads.

"What you have at the moment is confusion," said Harper, citing Russia as an example. "On the one hand, you have Trump who would like to do a deal with Putin, including the Ukraine and perhaps recognizing Russia's sovereignty over Crimea and then fight terrorism in the Middle East with Russia. And then you have the other group who wants to be tough on Russia and Iran and to pursue a more aggressive policy towards both."

Trump's trust

Wickett argued that the differences between Trump and Mattis and between Mattis and Flynn are not necessarily a bad thing, especially as long as he has Trump's trust. "Perhaps Mattis can have an influence on changing Trump's views in some areas," she said.

Especially on the nuclear Iran agreement, which Trump and Flynn as well as Trump's pick to head the CIA, Mike Pompeo, want to get rid off, Mattis could play a mediating influence, noted Wickett.

To be sure, she said, Mattis is no fan of the Iran deal and favors a tough stance on Tehran. "But on the Iran deal he is also more nuanced," Wickett said. "He has huge distrust of Iran so you can see him trying to walk a line that accepts that the deal is done, but puts a lot of effort into verification and trying to ensure that Iran continues to live by the deal and more."

Wickett's hope that Mattis could bridge ideological differences and prevent the US from nixing the Iran deal is shared by Harper.

"That's the chief risk at the moment that they will try to tear up or in some way undermine the nuclear agreement and provoke Iran," he said. "I think that would be very dangerous, also for American-European relations."