As fears grow that Russia will soon invade Ukraine, the Biden administration finds itself squaring off against a nuclear superpower with only limited military options to try to deter President Vladimir Putin.
The probability of an attack has “increased significantly” in the past two weeks, a US defence official said, pointing to an increase in Russian forces on the border with Ukraine and in Moscow-allied Belarus.
“They’re deploying multiple-domain capabilities without any sign of de-escalation” the official told The National.
Defence Secretary Lloyd Austin briefed Mr Biden at Camp David at the weekend on some of the options available for Washington should Moscow launch an attack.
The Pentagon then announced it is putting 8,500 troops on standby to join a Nato response force in the event of an attack.
“This is really about reassuring the eastern flank of Nato … [Mr Austin] wants us postured to be ready for any other contingencies as well,” Pentagon spokesman John Kirby said.
And US Deputy Secretary of State Wendy Sherman on Wednesday said an invasion could come by mid-February.
But Mr Biden has stressed no US forces will be deployed into Ukraine, which is not a Nato member.
“There is not going to be any American forces moving into Ukraine,” Mr Biden said on Tuesday.
Mark Cancian, senior adviser at the Centre for Strategic and International Studies (CSIS), saw no strong rationale for the US to intervene directly in Ukraine.
“We have no treaty with Ukraine, we are not obligated to defend Ukraine, and they are not a member of Nato,” Mr Cancian, a retired US Marine colonel, told The National.

The doomsday scenario of a nuclear confrontation or the risk of drawing the US into a conflict on Russia’s border make any direct military intervention unappealing. With about 127,000 Russian forces massed along the Ukrainian border, Mr Cancian described any US force deployment to Ukraine as “an invitation for disaster".
Instead, Mr Cancian saw the 8,500 US troops as sending a signal to Mr Putin, who is loath to see US and Nato forces on his doorstep.
Other options include increasing lethal aid, training missions and intelligence sharing with Ukraine, Mr Cancian said.
CNN reported last week that the CIA is operating an intelligence collection training programme on US soil for Ukrainian special operators and intelligence officials.
The Biden administration announced this month that it is providing additional $200 million in military aid to Kiev. Since the Russian annexation of Crimea in 2014, the US has provided Ukraine with about $2.5bn in security assistance, most of it considered “non-lethal”, such as training and defensive weaponry.
A US plane carrying Javelin anti-tank missiles, launchers and other military hardware arrived in Kiev on Tuesday.
Last week, the State Department gave Latvia, Estonia and Lithuania the go-ahead to send anti-armour missiles to Ukraine.
Other analysts see a need for the US to provide Kiev with sophisticated weaponry such as man-portable air defence systems as well as counter-UAV capabilities.
“The administration should be moving heaven and earth to urgently provide Ukraine — a beleaguered democracy pleading for American help — with the weapons and other support it needs to deter a Russian offensive by increasing the costs of aggression for the Kremlin,” Bradley Bowman, John Hardie and Jack Sullivan of the Foundation for Defence of Democracies said in a recent paper.
They argued that the Biden administration should do now what it should have done in November, when Mr Putin's invasion plans first came to light.
Mr Biden should “move with a sense of urgency to provide Kiev with additional defensive weapons and other support".
“The goal should be to help Ukrainian forces survive Russia’s initial air and missile assault, and to make clear to Putin that Russian forces would suffer major losses during an invasion and potential follow-on occupation,” they wrote.
Such options would increase Ukraine’s military capability but are not necessarily game-changers, Samuel Charap and Scott Boston of the RAND Corporation argued.
“The only weapons systems that could plausibly impose costs that could change Russia's calculus, such as surface-to-air missiles and combat aircraft, are ones that the United States would be highly unlikely to provide the Ukrainians,” they wrote last week.
The US is wary of antagonising Russia by sending such weaponry. But given the current crisis, US politicians from both parties have stepped up calls to allow supplying Kiev with surface-to-air missiles and defence systems.