WASHINGTON (NYTIMES) - In the chaotic finale of America's 20-year war in Afghanistan, a Biden doctrine is emerging: a foreign policy that avoids the aggressive tactics of forever wars and nation-building, while uniting allies against the authoritarianism of rising powers.

President Joe Biden began to define this doctrine last Tuesday (Aug 31) when he declared the end of "an era of major military operations to remake other countries", offering what he said was a better way to protect American interests around the world through diplomacy, the military's targeted anti-terrorism abilities and forceful action when necessary.

But the disordered ending to the war has laid bare the strains inherent in Mr Biden's foreign policy, which calls for a return to protecting human rights and promoting democracy, but only when consistent with United States goals.

The President's withdrawal from Afghanistan makes clear that he saw risking more US lives there as no longer in America's national interest.

"At some level, he seems to be applying a standard of if I wouldn't send my child to this war, then as president I shouldn't be asking anyone else to send their children," said Ms Michele Flournoy, a former undersecretary of defence during the Obama administration.

"Frankly, that's a standard we should expect every president to apply."

But, she added: "It's important to draw a distinction between his appetite for nation-building, which is essentially nil, versus his appetite for using force if it's necessary to defend US national security, which I believe remains quite strong."

The Biden doctrine sees China as America's existential competitor, Russia as a disrupter, Iran and North Korea as nuclear proliferators, cyber threats as ever-evolving and terrorism as spreading far beyond Afghanistan.

In White House meetings on many of those issues, the President has indicated that he is comfortable with the idea of backing US diplomacy with a muscular military posture, administration officials said.

He is eager to remind Iran of America's strike abilities, as he did last month when he said in public remarks during a meeting with Prime Minister Naftali Bennett of Israel that if diplomacy failed to rein in Iran's nuclear ambitions, he was "ready to turn to other options".

But such threats only work if adversaries believe he will follow through.

Mr Biden has ordered military strikes in Syria against Iranian-backed Shi'ite militias that rocketed US troops in Iraq, and, more recently, in Afghanistan against the Islamic State in Iraq and Syria (ISIS) terror outfit after the group took responsibility for a suicide bombing at the Kabul airport.

But those attacks were retaliation against non-state actors and not intended to be followed by US troops on the ground.

After the President's clear delineation of his distaste for US military involvement overseas, "nobody believes that the Biden administration is going to attack the Iranian nuclear programme", said Dr Kori Schake, who directs foreign and military policy studies at the conservative American Enterprise Institute and served in the Pentagon under President George W. Bush.

"That would have sustained military ramifications."

Mr Biden's aversion to protracted nation-building efforts is not new.

As a senator, he voted in favour of the Afghanistan and Iraq wars, but soon soured on the endeavours.

As vice-president in the Obama administration, he pressed forcefully for the US to draw down troops.

With the exception of the Pentagon, where officials argued against Mr Biden's Afghanistan withdrawal, the President has surrounded himself with longtime national security aides who helped shape his view of how to advance American interests abroad.

Mr Antony Blinken, now secretary of state, was on his staff when he was a senator as well as when he was vice-president.

Mr Jake Sullivan, the national security adviser, also counselled Mr Biden in the Obama administration.

Even Mr Colin Kahl, the Pentagon's undersecretary of defence for policy, is a former Biden hand; he, too, had a stint as national security adviser to Mr Biden when he was vice-president.

The result, critics say, is that Mr Biden's doctrine is being formed by a group of like-minded officials, most of them largely on the same page as their boss.

That unity means it is more difficult for allies and adversaries to exploit differences in the administration.

But it also means the President may not be stress-testing his doctrine during internal meetings at the White House.

Nowhere will a stress test be more necessary than on China, which presents a military, economic and technological challenge.

The administration is seeking to counter the narrative of a surging power and a declining America by showcasing a US economic recovery.

For that to work, Mr Biden must rein in the coronavirus pandemic, but without the authoritarian tools that are available to Beijing.

Last month, Mr Blinken warned that China and Russia were "making the argument in public and in private that the United States is in decline - so it's better to cast your lot with their authoritarian visions for the world than with our democratic one".

A strong economic recovery in the US may help, but the President is also seeking to hold off Chinese aggression in the South China Sea, where Beijing has militarised a number of disputed islands.

And then, there is Taiwan, the issue administration officials and national security experts agree is most likely to tip the scales from power struggle to military conflict.

At the White House, the State Department and the Pentagon, officials are trying to figure out if the longtime US policy of "strategic ambiguity" - providing political and military support to Taiwan, while not explicitly promising to defend it from a Chinese attack - has run its course.

Pentagon officials say the matter could come to a head within six years.

On Russia, Mr Biden will certainly be tougher than his predecessor, President Donald Trump, who ceded to President Vladimir Putin on several fronts.

In particular, Mr Biden has pressed the issue of Russia's interference in US elections and warned in a speech in July that cyber attacks emanating from Russia could lead to a "real shooting war with a major power".

He has also taken a tougher line than Mr Trump in backing allies against Russia. But there again, Mr Biden has set a stage for diplomacy bolstered by potential American force.

President Volodymyr Zelensky of Ukraine finally got the Oval Office visit he had been wanting last Wednesday, after his efforts to secure such a meeting with Mr Trump became entangled in an episode that led to the American's first impeachment.

Mr Biden assured Mr Zelensky that the US remained opposed to Russian aggression in the region.

The messy exit from Afghanistan, however, has left Ukraine and other European allies fearful that their reliance on American power might be misplaced.

The European Union's foreign policy chief, Mr Josep Borrell, described the departure as "a catastrophe for the Afghan people, for Western values and credibility and for the developing of international relations".

Not lost on US allies is the fact that, for all of the criticism Mr Biden has received for the Afghan withdrawal, the American public still supported it.

"Whether it is a Republican or Democratic president, as we saw with Trump, there is this exhaustion with major missions that put large numbers of troops on the ground and have ambitions to remake the governments in countries," said Ms Lisa Curtis, who oversaw policy for Afghanistan and elsewhere in Central and South Asia on the National Security Council during the Trump administration.

She said Mr Biden was "well in step with the American public".

One place where Mr Biden has indicated he will use the military forcefully and quickly is on counter-terrorism.

"We will hunt you down and make you pay," he vowed after a suicide attack on the airport in Kabul killed more than 170 people, including 13 US service members.

Hours later, an American drone struck a vehicle in Nangarhar province, killing two ISIS operatives.

Two days after that, another US airstrike took out a vehicle and its driver, who the Pentagon said intended to carry out another attack on the Kabul airport.

As many as 10 civilians may also have been killed in that strike, an Afghan family has said.

Twenty years of military action by the US and its international partners have exacted major tolls on Al-Qaeda and ISIS, killing many of their fighters and leaders and largely preventing them from holding territory.

But both groups have proved able to adapt, terrorism experts say, evolving into more diffuse organisations.

Mr Biden's doctrine calls for conducting operations against the groups from afar, or "over the horizon".

That means fewer US service members killed in the process, the Pentagon hopes.

But that also means fewer Americans on the ground to gather intelligence and call in such strikes.

Mr Vali Nasr, a senior State Department policy adviser during the Obama administration, said there was no reason to believe the President would resist sending US troops into conflict when warranted.

"I don't read this as Biden saying that we will never go to war at all," he said.

Still, "I think for him, the idea of the forever war, of these Middle East wars where we basically go down a rabbit hole after the target without actually achieving much, is going to lock us in and take away from us the ability to address other sets of issues", Mr Nasr said.

But the first test for the Biden doctrine may yet be Afghanistan, as terrorists from around the world are likely to feel safe relocating to a country "where their brothers in arms" are in charge, Ms Curtis said.

Mr Biden "was very clear that he did not believe that we needed boots on the ground to protect US counter-terrorism interests", she said.

But, she added, "the war against terrorism has not ended".