WASHINGTON (AP) — President Donald Trump starts the new year knee-deep in daunting foreign policy challenges at the same time he'll have to deal with a likely impeachment trial in the Senate and the demands of a reelection campaign.

American troops are still engaged in America's longest war in Afghanistan. North Korea hasn't given up its nuclear weapons. Add to that simmering tensions with Iran, fallout from Trump's decision to pull troops from Syria, ongoing unease with Russia and Turkey, and erratic ties with European and other longtime Western allies.

Trump is not popular overseas, and being an impeached president who must simultaneously run for reelection could reduce the time, focus and political clout needed to resolve complex global issues like North Korea's nuclear provocations. Some foreign powers could decide to just hold off on finalizing any deals until they know whether Trump will be reelected. Trump himself has acknowledged the challenge in his Dec. 26 tweet:

"Despite all of the great success that our Country has had over the last 3 years, it makes it much more difficult to deal with foreign leaders (and others) when I am having to constantly defend myself against the Do Nothing Democrats & their bogus Impeachment Scam. Bad for USA!"

At the same time, there is widespread expectation that Trump never will be convicted by the Republican-controlled Senate, so 2020 could well bring more of the same from the president on foreign policy, said Ronald Neumann, president of the American Academy of Diplomacy.

"America still has an awful lot of power," said Neumann, a three-time ambassador and former deputy assistant secretary of state. "With a year to go, a president can still make a lot of waves, impeachment or not."

For Trump, 2019 was a year of two steps forward, one step back — sometimes vice versa — on international challenges. Despite claiming that "I know deals, I think, better than anybody knows deals,'' he's still trying to close a bunch.

Trump scored high marks for the U.S. military raid in Syria that killed the leader of the Islamic State, but U.S. military leaders worry about a resurgence. He is credited with coaxing NATO allies to commit to spend billions more on defense, but along the way has strained important relationships.

His agreement on a "Phase 1" trade deal with China has reduced tensions in their ongoing trade war. But the deal largely puts off for later complex issues surrounding U.S. assertions that China is cheating to gain supremacy on technology and China's accusation that Washington is trying to restrain Beijing's ascent as a world power.

A deeper look at the state of play on three top foreign policy challenges on Trump's desk as 2020 begins:

US-NORTH KOREA NUCLEAR TALKS LOSE TRACTION

The U.S. is watching North Korea closely for signs of a possible missile launch or nuclear test.

Pyongyang had threatened to spring a "Christmas surprise" if the U.S. failed to meet Kim Jong Un's year-end deadline for concessions to revive stalled nuclear talks. Trump speculated maybe he'd get a "beautiful vase" instead. Any test flight of an intercontinental ballistic missile or substantial nuclear test would further derail the diplomatic negotiations Trump opened with Kim in 2018.

Washington didn't accept Kim's end-of-year ultimatum, but Stephen Biegun, the top U.S. envoy to North Korea, said the window for talks with the U.S. remains open. "We are fully aware of the strong potential for North Korea to conduct a major provocation in the days ahead," Biegun, the new deputy secretary of state, said recently. "To say the least, such an action will be most unhelpful in achieving lasting peace on the Korean Peninsula."

In recent months, North Korea has conducted a slew of short-range missile launches and other weapons tests.

In 2017, Trump and Kim traded threats of destruction as North Korea carried out tests aimed at acquiring the ability to launch nuclear strikes on the U.S. mainland. Trump said he would rain "fire and fury" on North Korea and derided Kim as "little rocket man." Kim questioned Trump's sanity and said he would "tame the mentally deranged U.S. dotard with fire."

Then the two made up and met three times — in Singapore in 2018, in Vietnam last February and again in June when Trump became the first U.S. president to set foot into North Korea at the Demilitarized Zone.

While the get-togethers have made for good photo-ops, they've been devoid of substantive progress in getting Kim to get rid of his nuclear weapons.

Trump has held out North Korea's self-imposed moratorium on conducting nuclear tests and trials of long-range intercontinental missiles as a major foreign policy achievement. "Deal will happen!" he tweeted.

Trump's former national security adviser doesn't think so.

"The North Koreans are very happy to declare that they're going to give up their nuclear weapons program, particularly when it's in exchange for tangible economic benefits, but they never get around to doing it," John Bolton told National Public Radio.

US-IRAN TENSION ESCALATING

Tensions with Iran have been rising ever since Trump last year withdrew the U.S. from the 2015 nuclear deal that Tehran had signed with the U.S. and five other nations. Trump said the deal was one-sided and gave Iran sanctions relief for rolling back, but not permanently dismantling, its nuclear program.

After pulling out of the deal, Trump began a "maximum pressure" campaign, reinstating sanctions and adding more that have crippled Iran's economy. His aim is to force Iran to renegotiate a deal more favorable to the U.S. and other nations that are still in the agreement.

In response, Iran has continued its efforts to destabilize the region, attacking targets in Saudi Arabia, interrupting commercial shipping through the critical Strait of Hormuz, shooting down an unmanned U.S. aircraft and financing militant proxy groups. Since May, nearly 14,000 U.S. military personnel have deployed to the region to deter Iran.

Iranian President Hassan Rouhani said his country's nuclear experts are testing a new type of advanced centrifuge. Iran recently started exceeding the stockpiles of uranium and heavy water allowed by the nuclear deal and is enriching uranium at a purity level beyond what is permitted. Tehran's violations, which it says are reversible, are an attempt to get France, Germany, Britain, China and Russia — the other nations that signed the Joint Comprehensive Plan of Action — to offer new economic incentives to offset the American sanctions.

The White House says its pressure campaign is working. The Iranian economy is collapsing, inflation is high. And crushing U.S. sanctions blocking Iran from selling its crude oil abroad have helped fuel nationwide protests.

Earlier this month, there was a rare diplomatic breakthrough when a Chinese-American Princeton scholar, Xiyue Wang, who has held in Iran for three years, was freed in exchange for a detained Iranian scientist in the U.S.

Trump said the prisoner exchange could be a "precursor as to what can be done."

Iran says other prisoner swaps can be arranged, but there will be no other negotiations between Tehran and the Trump administration.

AFGHANISTAN

It's no secret that Trump wants U.S. engagement in Afghanistan to end, but critics have expressed concern about giving too many concessions to the Taliban or if they will honor any agreement that could end the fighting.

In what appeared to be a breakthrough Sunday, top Taliban leaders agreed to a temporary cease-fire nationwide, but didn't say when it would start or how long it would last. A cease-fire, however, could provide an opening for a Taliban peace agreement with the United States that would let Trump bring U.S. troops home from Afghanistan, where they have fought for more than 18 years.

The U.S. wants any deal to include a promise from the Taliban that Afghanistan would not be used as a base by terrorist groups. A key part of a pact would include the Taliban agreeing to participate in all-Afghan negotiations to decide what a post-war Afghanistan would look like.

Such negotiations are expected to be contentious and touch on the rights of women, free speech and changes to the Afghan constitution. They also would determine the fate of tens of thousands of Taliban fighters and heavily armed militias run by Afghan warlords who have amassed wealth and power since the Taliban was ousted from power after 9/11.

"We'll see if they want to make a deal," Trump told U.S. troops on Thanksgiving Day when he visited Afghanistan for the first time. "It's got to be a real deal, but we'll see. But they want to make a deal."

Former Defense Secretary James Mattis, who resigned from the Trump administration over his opposition to the president's decision to remove troops from Syria, said the Taliban have not proven trustworthy in the past so instead of "trust and verify," the U.S. should "verify and then trust."

But he added: "I think the president was right to start the negotiations with the Taliban and I think he was right to call it off when the bombings occurred."' Trump canceled the talks in September when violence didn't abate during U.S. talks with the Taliban.

And even as the militants agreed to a cease-fire, an attack in northern Afghanistan killed at least 17 on Sunday and last week an American soldier was killed in a roadside bombing, also in the north.

Sen. Lindsey Graham, R-S.C., who visited Kabul this month, said Trump might announce an American troop drawdown from Afghanistan before year's end. Graham said that beginning next year, the president could reduce the 12,000 U.S. troops to 8,600, which he thinks is enough to make sure that Afghanistan doesn't become a launching pad for another 9/11-style attack on the U.S. The Taliban have said any peace agreement must include getting all American troops out of the country, where more than 2,400 American service members have been killed.