For the rest of December, Washington Examiner reporters will be exploring what 2018 has in store in a number of areas, from the White House and Congress to energy and defense. See all of our year ahead stories here.

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For the Pentagon, 2017 held the promise of new strategies backed by new resources, driven by fresh thinking and clear-eyed resolve. In 2018, we'll likely find out if those confident predictions will hold up when tested by the harsh realities of an increasingly complex word.

In Iraq and Syria, Trump’s approval of new authorities and tactical adjustments paid off, shifting the counter-Islamic State campaign into overdrive and crushing the group's once-expansive caliphate by year's end.

But while Iraq appears on a path to reconciliation and reconstruction, Syria remains a country where Bashar Assad, a brutal dictator who murdered hundreds of thousands of his own people, remains firmly propped up by Russia, which has extended its influence in what was once just a small foothold in the Middle East.

The U.S. is putting its hopes in a U.N.-brokered peace process, which so far has produced no results. The U.S., when there are no more ISIS fighters to fight, will have to decide whether to abandon its erstwhile allies or take sides in the conflict. That's in contrast to Russia, which is in Syria at the invitation of Assad.

There is probably no greater test of whether Trump was right to override his instincts and follow the advice of his national security team than his decision to double down in Afghanistan.

The president, ready to throw in the towel after watching 16 years of fighting, was slowly persuaded by his defense secretary, his Joint Chiefs chairman, and his national security adviser that by taking the gloves off, the Taliban could be humbled the same way ISIS was beaten in Iraq and Syria.

But if Afghanistan remains a stalemate one year from now, it’s hard to see the president signing on for more of the same when his gut told him to get out.

Russia and China, identified as rival powers in Trump’s new national security strategy, each present unique challenges in cooperation.

Trump needs China to help ratchet up sanctions to the point where North Korea’s already moribund economy is in danger of collapsing entirely and taking Kim Jong Un with it. Nothing less it seems will convince the North Korea leader that only by giving up his weapons, can his regime survive.

In dealing with Russia, the conundrum for Trump is how to work with a very willing Vladimir Putin, without feeding into the narrative of his critics, fueled by the Russia investigation, that he’s the Russian president’s toadie.

Iran is demonstrating that it, too, is a missile threat, and the Trump administration is looking for ways to expand restrictions on Iran’s missile program while improving the nuclear agreement, which Trump has called “a disastrous, weak and incomprehensibly bad deal.”

But by far the most daunting and dangerous dilemma facing the president is how to make good on his promise to force North Korea to give up its nuclear weapons, without sparking an all-out war with the potential for millions of casualties on both sides. Trump has drawn an uncompromising line in the sand and promised to take “all necessary” steps to achieve the denuclearization of the Korean Peninsula. “It will be taken care of,” he has vowed. “We have no choice.”

Rebuilding at home

The coming year will also be a key test of the president’s vision of a much larger and more powerful U.S. military and will show whether Washington is willing to pony up the money to achieve it.

During his first weeks in office, Trump pledged one of the “greatest military buildups in American history.” It echoed his campaign platform of building a 350-ship Navy out of the current 279 battle force ships and grow the Army to 540,000 active-duty soldiers from its current 476,000.

The president’s subsequent defense budget request released in May bumped up spending 5.5 percent over last year.

Analysts were quick to point out it would not be enough to grow the military. Meanwhile, the Pentagon acknowledged the promised buildup will be delayed for a year and defense hawks in Congress have worked to hike spending over the White House plan.

All eyes are now on February when Trump’s new fiscal 2019 defense budget is due, though the administration could still blow past that deadline.

Any buildup will depend on two budget figures — the top-line defense spending for the fiscal year and the projected spending growth over the coming five years, called the Future Years Defense Program.

“That’s the battle that is going on between DOD and [the White House Office of Management and Budget] is what kind of top-line growth do they get in the future,” said Todd Harrison, the director of defense budget analysis at the Center for Strategic and International Studies.

Defense Secretary Jim Mattis has said the military needs 3 percent increases above the 2 percent rate of inflation through 2023 just to maintain the status quo. But to grow the force and buy the Navy fleet envisioned by Trump will require more than 5 percent annual growth over those years.

“I think they are right if you want to get on the trajectory to grow the size of the force like they do,” Harrison said.

OMB Director Mick Mulvaney, who headed up Trump’s first budget request, projected no growth above inflation over the coming five years and also planned to reduce money for overseas contingency operations, a war account that is immune to spending caps and has been increasingly crucial to the military for funding daily operations, Harrison said.

Mattis and the Pentagon had essentially ignored the future plans as a placeholder and said they were focusing on just the year ahead. Now, as the Pentagon wraps up key strategy, nuclear and ballistic missile reviews, Mattis and the White House will soon need to settle on how to much money will go to defense.

“I’m not totally convinced Mattis and Mulvaney have come to an agreement on the top line. If the top line is still in play, then the budget is going to be pretty far from being locked,” Harrison said. “If we are starting to hear things that it is not locked then that is an early warning that [Trump’s defense budget request] may not be ready in time for the first Monday in February.”