WASHINGTON (NYTIMES) - United States relations with China are the worst since the countries normalised ties four decades ago.

America's allies in Europe are alienated.

The most important nuclear anti-proliferation treaty is about to expire with Russia.

Iran is amassing enriched nuclear fuel again, and North Korea is brandishing its atomic arsenal.

Not to mention global warming, refugee crises and looming famines in some of the poorest places on earth, all amplified by the pandemic.

President-elect Joe Biden is inheriting a landscape of challenges and ill will towards the United States in countries hostile to President Donald Trump's "America First" mantra, his unpredictability, embrace of autocratic leaders and resistance to international cooperation.

Mr Biden also could face difficulties in dealing with governments that had hoped for Mr Trump's re-election - particularly Israel and Saudi Arabia, which share the President's deep antipathy towards Iran.

But Mr Biden's past as head of the Senate Foreign Relations Committee and as vice-president in the Obama administration has given him a familiarity with international affairs that could work to his advantage, foreign policy experts who know him say.

"President Trump has lowered the bar so much that it wouldn't take much for Biden to change the perception dramatically," said Mr Robert Malley, chief executive of the International Crisis Group and a former adviser in the Obama White House.

"Saying a few of the things Trump hasn't said - to rewind the tape on multilateralism, climate change, human rights - will sound very loud and significant."

Here are the most pressing foreign policy areas the Biden administration will face.

The challenge of US-China relations

Nothing is more urgent, in the eyes of many experts, than reversing the downward trajectory of relations with China, the economic superpower and geopolitical rival that Mr Trump has engaged in what many are calling a new Cold War.

Disputes over trade, the South China Sea, Hong Kong, Taiwan and technology have metastasised during Mr Trump's term, his critics say, worsened by the President's racist declarations that China infected the world with the coronavirus and should be held accountable.

"China is kind of the radioactive core of America's foreign policy issues," said Mr Orville Schell, director of the Asia Society's Centre on US-China Relations.

Mr Biden has not necessarily helped himself with his own negative depiction of China and its authoritarian leader, President Xi Jinping, during the 2020 campaign.

The two were once seen as having developed a friendly relationship during the Obama years. But Mr Biden, perhaps acting partly to counter Mr Trump's accusations that he would be lenient towards China, has recently called Mr Xi a "thug".

The Middle East: Shifts on Israel, Saudi Arabia and Iran?

Mr Biden has vowed to reverse what he called the "dangerous failure" of Mr Trump's Iran policy, which repudiated the 2015 nuclear agreement and replaced it with tightening sanctions that have caused deep economic damage in Iran and left the US largely isolated on this issue.

Mr Biden has offered to rejoin the agreement, which constricts Iran's nuclear capabilities if Iran adheres to its provisions and commits to further negotiations. He also has pledged to immediately nullify Mr Trump's travel ban affecting Iran and several other Muslim-majority countries.

Whether Iran's hierarchy will accept Mr Biden's approach is unclear.

Iran's supreme leader, Ayatollah Ali Khamenei, has said that the US is untrustworthy regardless who is in the White House.

At the same time, "Iran is desperate for a deal", said Mr Cliff Kupchan, chairman of the Eurasia Group, a political risk consultancy.

Still, Mr Kupchan said, Mr Biden will face enormous difficulties in any negotiations with Iran aimed at strengthening restrictions on its nuclear activities - weaknesses that Mr Trump had cited to justify renouncing the nuclear agreement.

"The substance will be tough; we've seen this movie, and it's not easy," Mr Kupchan said. "I think Biden's challenge is that it will not end up blowing up in his face."

Mr Biden's Iran policy could alienate Israeli Prime Minister Benjamin Netanyahu, who leveraged Mr Trump's confrontational approach to help strengthen Israel's relations with Gulf Arab countries, punctuated by normalisation of diplomatic ties with the United Arab Emirates and Bahrain. How Mr Biden manages relations with Saudi Arabia, which considers Iran an enemy, will also be a challenge.

"There's a very hard square to circle here," Mr Kupchan said.

Mr Trump's extremely favourable treatment of Israel in the protracted conflict with the Palestinians also could prove nettlesome as Mr Biden navigates a different path in the Middle East. He has criticised Israeli settlement construction in occupied lands the Palestinians want for a future state. And he is likely to restore contacts with the Palestinian leadership.

"Benjamin Netanyahu can expect an uncomfortable period of adjustment," Israeli columnist Yossi Verter wrote on Friday (Nov 6) in the Haaretz newspaper.

At the same time, Mr Biden also has a history of cordial relations with Mr Netanyahu. Mr Biden has said he would not reverse Mr Trump's transfer of the US Embassy in Israel to Jerusalem from Tel Aviv - a relocation that deeply angered the Palestinians.

Repairing relations with Europe and navigating Brexit

While Mr Trump often disparaged the European Union and strongly encouraged Britain's exit from the bloc, Mr Biden has expressed the opposite position. Like former president Barack Obama, he supported close US relations with bloc leaders and opposed Brexit.

Mr Biden's ascendance could prove especially awkward for British Prime Minister Boris Johnson, who had embraced Mr Trump and had been counting on achieving a trade deal with the US before his country's divorce from the bloc takes full effect.

Mr Biden may be in no hurry to complete such an agreement.

While many Europeans will be happy to see Mr Trump go, the damage they say he has done to America's reliability will not be easily erased.

"We had differences, but there was never a basic mistrust about having common views of the world," former Norway prime minister Gro Harlem Brundtland told The New York Times in October. Over the past four years, she said, European leaders had learnt they could "no longer take for granted that they can trust the US, even on basic things".

Confronting North Korea's nuclear threat

Mr Trump has described his friendship and three meetings with North Korea leader Kim Jong Un as a success that averted war with the nuclear-armed hermetic country. But critics say Mr Trump's approach not only failed to persuade Mr Kim to relinquish his arsenal of nuclear weapons and missiles, it bought Mr Kim time to strengthen them.

In October, North Korea unveiled what appeared to be its largest intercontinental ballistic missile (ICBM).

"On Trump's watch, the North's nuclear weapons programme has grown apace, its missile capabilities have expanded, and Pyongyang can now target the United States with an ICBM," said Mr Evans Revere, a former State Department official and expert on North Korea. "That is the legacy that Trump will soon pass on to Biden, and it will be an enormous burden."

Mr Biden, who has been described by North Korea's official news agency as a rabid dog that "must be beaten to death with a stick", has criticised Mr Trump's approach as appeasement of a dictator.

Mr Biden has said he would press for denuclearisation and "stand with South Korea" but has not specified how he would deal with North Korean belligerence.

A likely tougher approach to Russia and Putin

Mr Biden has long asserted that he would take a much harder line with Russia than Mr Trump, who questioned the usefulness of the North Atlantic Treaty Organisation, doubted intelligence warnings on Russia's interference in US elections, admired President Vladimir Putin and said that improving US relations with the Kremlin would benefit all.

Mr Biden, who as vice-president pushed for sanctions against Russia over its annexation of Ukraine's Crimean peninsula in 2014 - the biggest illegal land seizure in Europe since World War II - might seek to extend those sanctions and take other punitive steps.

While tensions with Russia would likely rise, arms control is one area where Mr Biden and Mr Putin share a desire for progress.

Mr Biden is set to be sworn in just a few weeks before the scheduled expiration of the 2010 New Strategic Arms Reduction Treaty. He has said he wants to negotiate an extension of the treaty without preconditions.

A return to the Paris Agreement and international commitments

Mr Biden has said one of his first acts as president will be to rejoin the Paris Climate accord to limit global warming, which the US officially left under Mr Trump on Wednesday. Mr Biden also has said he would restore US membership in the World Health Organisation, which Mr Trump repudiated in the midst of the coronavirus pandemic, describing the WHO as a lackey of China.

More broadly, Mr Biden is expected to reverse many of the isolationist and anti-immigrant steps taken during the Trump administration, which are widely seen by Mr Trump's critics as shameful stains on America's standing in the world.

Mr Biden has said he would disband Mr Trump's immigration restrictions, stop construction of his border wall with Mexico, expand resources for immigrants and provide a path to citizenship for people living in the United States illegally.

Nonetheless, many of Mr Trump's policies had considerable support in the US, and it remains to be seen how quickly or effectively Mr Biden can change them. The convulsions that roiled American democracy and the divisive election have also sown doubts about Mr Biden's ability to deliver on his pledges.

"There is relief at a return to some kind of normalcy, but at the same time, history cannot be erased," said French diplomat Jean-Marie Guehenno, who is a fellow at the Brookings Institution's Foreign Policy Programme and a former undersecretary-general for peacekeeping operations at the United Nations.

"The kind of soft power that the United States has enjoyed in the past has largely evaporated," he said.