For President Trump, the easy part is over.
During the 2016 campaign, Trump slammed the U.S. national security and foreign policy establishment as run by people who were "so dumb," "predictable" and played for "a bunch of suckers."
Now he owns it.
Trump's inauguration makes him responsible for responding to hot spots and crises around the world — challenges that scale from the risk of an individual terrorist attacking inside the U.S. to the danger of a nuclear standoff with Russia.
The new president is still assembling the team that will help him. Incoming White House press secretary Sean Spicer said last Thursday the new administration has asked more than 50 senior deputy and assistant leaders to stay in place through the transition, including Deputy Defense Secretary Bob Work; Brett McGurk, the top U.S. envoy for the fight against ISIS, and Nick Rasmussen, the head of the National Counterterrorism Center.
As the Trump team continues to take shape, here are seven tough international challenges it will face.
1. North Korea
The Defense Department won't confirm press reports that North Korea could soon test-fire a ballistic missile that might be capable of hitting the U.S. with a nuclear warhead.
But Pentagon press secretary Peter Cook said the military would be "ready" no matter what. He urged Pyongyang not to misread the change of authority in the U.S. as an opening to make what he called a "provocative act."
"We'll continue to be prepared as we go through this transition," Cook said.
North Korea has demonstrated that it can detonate nuclear weapons and that it can fire ballistic missiles. It's now trying to build a weapon small enough to fit on a missile effective enough to hit the U.S. or on one of its existing rockets that could target South Korea or Japan.
The U.S. has treaty alliances with both nations, and they host some 80,000 U.S. troops. Although the North has attempted and failed launches in the past, national security watchers in Washington warn that the unsuccessful tests are ultimately productive because they help Pyongyang learn.
As NPR's Mary Louise Kelly reported, intelligence officers in Washington warn the North Korea nuclear missile threat is the one that doesn't get enough attention.
2. China
Trump's dealings with China might be the most consequential bilateral relationship of his presidency, given the size of the economic, diplomatic and military intricacies.
They're off to a rocky start. Beijing was angry about Trump's pre-inauguration phone call with the president of Taiwan — which was seen as a challenge to the long-standing "One China" policy.
Then there was the seizure of a U.S. underwater drone from an oceanographic survey ship that helps the U.S. Navy search for foreign submarines. China returned the "glider" after Washington demanded it back, but it was another reminder by Beijing that it considers the East and South China Seas its own, even though the U.S. and the other countries in the neighborhood say they are international waters with competing claims.
China has been building up reefs and creating artificial islands in the area to bolster its claims of ownership. Washington says none of that construction changes the laws that keep the waterways open. But tension seems likely to remain a recurring theme.
3. Afghanistan
Trump and his new aides have barely spoken about their plans for America's longest-ever war, which has now gone on for more than 15 years.
Barack Obama hoped he could end his presidency with only a small detachment of U.S. troops there, but gains by the insurgent Taliban forced him to freeze the planned drawdown and hand Trump a deployment of more than 8,500 troops. New combat units are gearing up to deploy to Afghanistan this year to fight insurgents for ground the U.S. has already gained and lost, especially in the south.
The dilemma is that Afghanistan's government probably can't survive without American financial and military support. Trump suggested in an interview last summer that the security situation might mean he had no choice but to continue with the open-ended American deployments to Afghanistan.
"I think you have to stay and do the best you can," he told Bill O'Reilly on Fox News. "Not that it's ever going to be great, but I don't think we have much of a choice."
4. Iraq
The Pentagon says Iraq's army — with significant American support — is making progress in its fight against the Islamic State. The terrorist group is at risk of losing its northern stronghold in Mosul, the last city that is even partly under its control.
But even if the heavy fighting ends in Iraq, there will be political challenges for the U.S., the central government in Baghdad and the Kurdish regional government based in Irbil.
Who will be in charge? Who will provide security? What role will neighboring Turkey and Iran play in Iraq? Can Iraq's mostly Shiite government provide credible governance to the Sunni areas?
If Iraq reverts to the sectarian divisions so prevalent before the rise of ISIS, that could undermine any battlefield victory over the extremist group.
5. Syria
The buildup of forces has begun for an assault on the Islamic State's capital of Raqqa, in northern Syria. With no support from the host government and no major nearby bases from which to support the combatants, the effort depends on small groups of American special operators training and arming thousands of local Kurdish and Arab fighters.
The Pentagon under Obama said it was confident it could make the effort work, but Trump and his choice for defense secretary, retired Gen. James Mattis, may seize the opportunity to step things up. Mattis recently said he wanted to "energize" the war.
Mattis did not give specifics, but the U.S. could, for example, give American warplanes greater latitude in attacking ISIS — although that could also bring greater risks of civilian casualties. Or the new administration could deploy more U.S. forces beyond the current 600 or so special operators now in Syria.
The potential upside is that more American power could deal a decisive blow to ISIS. The potential downsides are the risks to American forces and local populations, and the ultimate question about what comes next — whether the U.S. would wind up trying to extricate itself from another Middle Eastern war.
6. Libya
Since the Sept. 11, 2001, attacks, the U.S. has deplored "ungoverned spaces" around the world. Yet the U.S. helped create another one in Libya, which has been lawless since 2011, when the U.S. and European military operations helped rebels oust dictator Moammar Gadhafi.
Libya has become a refuge for Islamic State fighters, and American troops have responded with airstrikes and other operations. The latest took place Jan. 18, when Air Force B-2 Spirit bombers killed an estimated 80 ISIS fighters in desert camps outside the coastal city of Sirte.
The U.S. is supporting one of the groups that hope to form a new government in Libya, but under Obama it did not make a major effort. Trump's team must decide how much energy it wants to expend on trying to establish order in Libya.
7. Eastern Europe
The nations of Eastern Europe are nervous. Russian forces invaded Ukraine in 2014, and others, including Poland and the Baltic States, worry they could be next in the crosshairs.
Trump says he wants a better relationship with Russia and that if, based on public comments, Russian President Vladimir Putin likes him, that's a plus. What Eastern European nations fear is they'll be the ones paying the price for any rapprochement.
Obama committed to new demonstrations of military support for the Eastern European members of NATO, including regular rotations of troops for training exercises. Trump must decide whether to keep that up. And he is facing renewed pressure from the NATO allies and some advocates inside the U.S. to go even further and commit to full, permanent military bases.
Senate Armed Services Committee Chairman John McCain, an Arizona Republican, asked Mattis at his confirmation hearing about whether he would support a "permanent military presence in the Baltics."
Mattis said he would. Squaring that outlook with Trump, along with Mattis' vocal support for NATO, will be one of the biggest stories of the first months of the new administration.
Trump himself is sanguine about the world scene he will encounter, as he told The New York Post this week.
"I don't think we're going to be tested," he said. "I'm not a game player. They understand me."
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