With roughly two months left in his presidency, Joe Biden has made a consequential policy decision that could escalate the war in Ukraine.

For months, Biden has dragged his feet on giving Ukraine permission to use the U.S. Army Tactical Missile System (ATACMS) to attack targets inside Russia. That changed this weekend when U.S. officials acknowledged that Biden had finally given Ukraine the green light to use the long-range missile system.

Concern over provoking Russian President Vladimir Putin into retaliating against NATO countries bordering Ukraine had prevented Biden from agreeing to Ukrainian President Volodymyr Zelensky’s repeated requests.

However, Biden’s calculations apparently changed following news that Russia was equipping 10,000 North Korean troops who are currently in Russia. Putin plans on using them in a push to regain Russia’s Kursk region, which Ukraine took and held in a surprise advance into Russia in August.

The ATACMS, which has an effective range of 190 miles, will help the Ukrainians target Russian and North Korean troops well behind the lines.

Zelensky acknowledged the recent development, stating in an address to the nation, “Today, there’s a lot of talk in the media about us receiving permission for respective actions. But strikes are not carried out with words. Such things are not announced. Missiles will speak for themselves.”

And like clockwork, Ukraine last night apparently used ATACMS to strike an ammunition depot in Karachev, which is in Russia about 75 miles from the Ukraine border.

If peace talks are to occur, Ukraine will want to use Kursk as a bargaining chip to force Russia to relinquish the Ukrainian lands it has taken in recent months. Some view the ATACMS green light as crucial to helping Ukraine in this endeavor.

Donald Trump has repeatedly expressed his intent to bring the war to an end quickly, but he hasn’t offered any specifics. The Trump team leaked that the president-elect had a call with Putin, during which he asked the Russian strongman not to escalate the war.

Apparently, Putin ignored that request, as the Russians launched a missile barrage over the weekend targeting Ukraine’s energy supplies just as winter approaches. This move, combined with Putin’s acceptance and deployment of North Korean troops, demonstrates that he has no intention of slowing things down. Indeed, Putin appears to be pressing the issue to strengthen his hand as much as possible before Trump takes office.

Biden’s green-lighting of the ATACMS is less likely to result in Putin striking out against NATO and seems to be a calculated risk. Putin, knowing that Trump will soon replace Biden and bring a new foreign policy with him, is unlikely to risk spreading the conflict beyond the borders of Russia and Ukraine.

Despite this, the Kremlin threatened a “nuclear response” if Ukraine used ATACMS to strike targets within Russia. “The Russian Federation reserves the right to use nuclear weapons in the event of aggression against it with the use of conventional weapons,” said Dmitry Peskov, the Kremlin’s press secretary.

The developments over the next couple of months — in Moscow, Kyiv, and Washington — will be telling as to whether the war will end anytime soon.