United States President Joe Biden has made unceasing support for Ukraine during Russia’s invasion a hallmark of his one-term presidency, using his office to funnel weapons and aid to Kyiv while wrangling Congress to keep the US purse strings loose.

But one issue has remained a key sticking point: Biden has refused to allow Ukraine to use US-provided, long-range Army Tactical Missile Systems (ATACMS) inside Russian territory amid warnings from Moscow that their use would represent the crossing of a red line.

But with just more than two months left in his term – and a second administration of US President Donald Trump looming – Biden’s government has pivoted on the policy, and Ukrainian and US officials told the Reuters news agency and several US media outlets that the weapons had been used in Russia for the first time.

Moscow also said on Tuesday that six ATACMS had been fired at its Bryansk region, in what it said represented a “new phase” in the war.

So why now?

Anatol Lieven, the director of the Eurasia Program at the Quincy Institute for Responsible Statecraft, pointed to three possible factors: The “more negative way of assessing this” is that the Biden administration is seeking to scuttle Trump’s promises to end the fighting; the “more positive” take is that the Biden administration is seeking to strengthen Ukraine’s hand before future negotiations; and the third alternative is that the policy change was needed to respond to shifting conditions on the ground.

“It’s rare that a decision of this kind is taken simply for one reason,” he said.

“My own feeling is that the Biden administration’s decision is a mixture of all these things.”

What has the Biden administration said?

The administration has not officially confirmed the policy change, but several officials have been detailing the move to US media.

Speaking to The Washington Post, two unnamed officials said the missiles would initially be used in and around Russia’s Kursk region, where Ukrainian troops have continued to hold land since launching a surprise incursion in August. It was not immediately clear if the missiles, which have a range of about 300km (190 miles), could be used elsewhere.

While Ukraine has requested clearance to use US weapons in Russia since early in the invasion, which began in February 2022, Ukrainian President Volodymyr Zelenskyy upped those appeals after the Kursk incursion. The Ukrainian military’s continued presence in the Russian territory is seen as a key point of leverage in any future negotiations with Russia.

Officials have told the Post and other US media that the change was largely motivated by Russia’s deployment of about 10,000 North Korean soldiers to the Kursk region as it pushes to expel Ukrainian forces. The move, they said, is meant to deter Pyongyang from sending any more of its forces to aid Russia.

Does this strengthen Ukraine’s hand before Trump’s second term?

It is no secret that the Biden administration and Trump have vastly diverging views on the future of the conflict in Ukraine.

Biden, a staunch believer in NATO, has promised perpetual support for Kyiv with the aim of eventually expelling Russia from Ukrainian territory. Trump has been sceptical of US aid to Kyiv – and of the NATO alliance as a whole – and has said he will pressure both Ukraine and Russia to end the war.

A Trump campaign adviser this month suggested the screws could be turned on Ukraine to relinquish at least some territory to Moscow as Trump’s ties with Russian President Vladimir Putin further stoke Kyiv’s disquiet.

The timing of the decision in the wake of the election may, therefore, be twofold, said Aaron David Miller, a senior fellow at the Carnegie Endowment for International Peace. It may strengthen Ukraine before future talks while upping the political stakes for Trump within his own party.

“Clearly, if the ATACMS, which I suspect will have limited influence in the overall trajectory of the conflict, help in holding off Russian advances in the Kursk region, it would obviously prove to be beneficial,” he said.

“There are still a substantial number of Republicans … who believe that defending Ukraine is within the broadest conception of American national interests,” he said.

Therefore, according to Miller, Trump may choose not to undo Biden’s ATACMS decision.

What have Trump’s allies said?

Unsurprisingly, Trump’s closest supporters have been unequivocal in their condemnation of the move. They broadly portrayed the shift as a cynical attempt to escalate the conflict as Trump prepares to take office.

In a post on X, Donald Trump Jr said the change was aimed at getting “World War 3 going before my father has a chance to create peace and save lives”.

Trump’s pick for national security adviser, US Representative Mike Waltz, called it “another step up the escalation ladder”.

“And nobody knows where this is going,” he said on Fox News.

Former Trump cabinet member Richard Grenell also accused Biden of moving to “escalate the war in Ukraine during the transition period”.

“This is as if he is launching a whole new war. Everything has changed now. All previous calculations are null and void,” he said.

What had changed on the battlefield before the decision?

But Michael O’Hanlon, senior fellow at the Brookings Institution, largely dismissed those claims, characterising the latest policy change as in line with previous Biden pivots on the war “with the same philosophy of delay and caution”.

The Biden administration had previously slow-rolled before eventually relenting to requests for M1 Abrams tanks and F-16 fighter jets to name a few. It had also resisted allowing Ukraine to use the High Mobility Artillery Rocket System (HIMARS), which has a range of about 65km (40 miles), inside Russian territory but later allowed its limited use to defend the Kharkiv region.

O’Hanlon pointed to the introduction of North Korean troops into the fight as the main reason for the change, adding that he did not see it as a departure from “the same basic Biden approach to the war over nearly three years”.

“If Russia escalates, we escalate,” he told Al Jazeera.

William Courtney, the former US ambassador to Georgia and Kazakhstan, also said the authorisation does not in and of itself represent a major escalation, particularly given supply constraints. Ukraine reportedly has received only a few dozen of the ATACMS systems.

“Ukraine is already attacking with its own drones targets much farther away than what the ATACMS can reach,” he said. “So this is not a whole new strategic shift, if you will. What ATACMS are good for, essentially, is time-urgent targets and targets that are heavily defended.”

US defence officials have noted that Russia has already moved many of its most sensitive targets out of ATACMS range.

Could this backfire for Biden?

Putin has for months warned that allowing Ukraine to strike inside Russia with Western-supplied weapons would transform the conflict dramatically.

“This will mean that NATO countries – the United States and European countries – are at war with Russia,” he said in September.

On Tuesday, Russia lowered its threshold for using nuclear weapons in an apparent response to the ATACMS attack.

The move has already sparked speculation that France and London could soon allow Ukraine to use their long-range SCALP and Storm Shadow cruise missiles, respectively, inside Russian territory.

Analysts gave Al Jazeera different assessments on just how risky the Biden move may be.

Given the limitations of the ATACMS, the Carnegie Endowment’s David Miller described the new authorisation as “probably the least risky thing [the Biden administration] could have done”.

Quincy’s Lieven also explained that Russia has an incentive to remain restrained until the Trump administration takes office.

He said direct confrontation with the US remains unlikely, but he did not rule out other responses, including sabotage aimed at an ally.

“The Russians have always really been afraid of letting one red line after another be crossed,” he said.

“So, yes, this is still extremely dangerous.”