President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE is facing an array of foreign policy challenges as 2018 starts winding down.

From deteriorating U.S.-Saudi relations to stalled denuclearization talks with North Korea, the Trump administration is finding itself fighting headwinds on the world stage.

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Trump is expected to flex his foreign policy muscles in 2019, when Democrats take control of the House, effectively constraining much of his domestic agenda.

In the meantime, here are five foreign policy challenges for the president:

Saudi Arabia

The furor over the killing of Washington Post writer Jamal Khashoggi ramped up this week after Trump suggested on Tuesday that Saudi Crown Prince Mohammed bin Salman is not to blame for the murder of the U.S.-based journalist.

Bipartisan anger among lawmakers was already on the rise, despite the Trump administration announcing sanctions last week against 17 Saudis for their alleged role in Khashoggi's death.

Members of Congress want Trump to punish Saudi Arabia and the crown prince, who they say ordered the killing of Khashoggi. The CIA reportedly reached the same conclusion regarding the crown prince, but Trump is siding with his denial that he was involved.

The president is hesitant to take steps that could damage U.S.-Saudi relations. He has fostered close ties with the crown prince and made the kingdom central to his Middle East strategy, one that includes pursuing an Israeli-Palestinian peace deal and countering Iran.

There is little sign that congressional pressure on Trump will let up anytime soon. A trio of senators is aiming to force a post-Thanksgiving floor showdown over the Saudi-led war in Yemen, and a bipartisan group of senators, including Trump ally Sen. Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.), recently introduced a bill aimed at pressuring Trump to levy harsher penalties against the Saudis.

North Korea

Trump has said he wants a second summit with North Korean leader Kim Jong Un next year, as a follow-up to the June meeting in Singapore. But the negotiations, aimed at getting North Korea to relinquish its nuclear weapons, have faced a series of setbacks.

North Korean state media recently touted Kim’s inspection of an “ultramodern tactical weapon” test. While it didn’t appeared to violate Pyongyang’s self-imposed moratorium on missile and nuclear tests, many viewed it as North Korea’s latest attempt to ramp up pressure on the United States. Pyongyang also threatened to reinstate its policy of a nuclear buildup if the United States does not lift sanctions.

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Further complicating matters is a report from a U.S. think tank this month that identified 13 undeclared missile operating bases in North Korea. That the bases exist is not a surprise, but it underscored Trump’s difficult task since they would “presumably have to be subject to declaration, verification and dismantlement in any final and fully verifiable denuclearization deal,” the report said.

Trump dismissed a New York Times write-up of the think tank’s report, calling it “just more fake news,” and arguing that “we fully know about the sites being discussed” and that there was “nothing happening out of the normal.”

Russia

Trump will meet with Russian President Vladimir Putin at the Group of 20 summit in Argentina at the end of the month. The two leaders initially considered meeting in Paris earlier this month when they both attended Armistice Day ceremonies, but instead only spoke to each other at a lunch alongside other world leaders.

Putin has said one of his top priorities for a meeting with Trump is to discuss arms control, particularly extension of the New START Treaty and revitalization of the Intermediate-range Nuclear Force (INF) Treaty.

New START is set to expire in 2021, but the treaty has the option to be renewed for five years.

Meanwhile, Trump has said he intends to withdraw from the INF Treaty over Russia’s alleged violations. But Trump has not issued a formal notice of withdrawal, leaving some to wonder if his announcement was a negotiating tactic.

Attempting to withdraw from the treaty would come amid a backdrop of increasing congressional opposition to Trump’s stated desire to improve U.S.-Russia relations. Also hanging over the president’s head is special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE’s investigation into possible collusion between Moscow and the Trump campaign during the 2016 presidential race. Publication of that report would undoubtedly influence U.S. policy toward Russia.

Iran

Trump’s plans to isolate Iran kicked into high gear this month when the remaining sanctions lifted under the 2015 nuclear deal were put back in place.

Trump announced in May that he was withdrawing the U.S. from the Obama-era international accord that gave Iran sanctions relief in exchange for curbs on its nuclear program.

The reimposition of sanctions is meant to pressure Iran back to the negotiating table to reach what Trump says will be a better deal for the United States. National security adviser John Bolton recently characterized the administration’s goal as wanting to squeeze Iran “until the pips squeak.”

Critics are skeptical Trump’s approach will work. Unlike the last time Iran negotiated, the international community is not backing U.S. sanctions.

Experts say Iran is banking on Trump being a one-term president and therefore has little incentive to negotiate during the next two years. International inspectors say Iran continues to abide by the terms of the 2015 accord.

Europe

U.S.-European tensions have escalated over trade, defense spending and a general difference in world views between Trump and the continent’s leaders.

That friction was on full display during Trump’s trip to Paris this month for Armistice Day. Almost immediately after landing, Trump slammed French President Emmanuel Macron in a tweet.

Then, during the Armistice Day ceremony, Macron took what appeared to be a thinly veiled shot at Trump, saying “patriotism is the exact opposite of nationalism.”

When Trump returned to the United States, he continued his Twitter criticisms, saying there is “no country more Nationalist than France” before complaining about France’s NATO contributions and trade policies.

The back-and-forth was a long way from the chumminess the two leaders displayed when Macron visited the White House in April.

Beyond politics, European leaders are also at odds with the United States over the Iran deal. Europe supports the international agreement, and the European Union is working on a way to allow companies to continue doing business with Tehran without getting hit with sanctions by the United States.