Russian President Vladimir Putin committed to a partial military mobilization in a speech Wednesday, where he also threatened nuclear retaliation against the West. It was a sign of Putin’s willingness to escalate the war in Ukraine, as Kyiv’s successful counteroffensive in the Kharkiv region has recaptured territory and pushed back Russian front lines.

Putin stopped short of decreeing a full national mobilization, instead only drafting the army reserves, a move he said was “necessary and urgent.” Russian Defense Minister Sergei Shoigu later confirmed that Russia would call about 300,000 reservists with previous military experience.

Putin also again made explicit threats against the West. “If its territorial integrity is threatened Russia will use all the means at its disposal,” he said. “This is not a bluff.” Putin warned that Russia “also has various means of destruction” — in other words, nuclear weapons — “and some components are more modern than those of the NATO countries.”

This is a particularly chilling threat, as Putin’s Wednesday address came shortly after Russian-backed officials in four Ukrainian regions partially occupied by Russian troops moved to hold referenda on formally joining Russia. Western countries backing Ukraine have already said they won’t recognize any votes, calling them total shams. The Russian army also does not have full control over any of these territories — Donetsk, Luhansk, Zaporizhzhia, and Kherson — but Moscow will almost certainly use these referenda as a pretext for formally annexing the territories. If that happens, as it’s expected to, some experts fear that Moscow will interpret any Ukrainian efforts to retake these lands as bringing the fight directly against Russia. The West has not supported Ukraine attacking Russian territory, but they have made clear these referenda are illegitimate.

All of this — the referenda, the partial military mobilization, and Putin’s renewed nuclear saber-rattling — are part of an effort to shake up a floundering war effort and to preserve his domestic standing.

“This wasn’t unexpected, because at this point, [Putin] is pushed into the corner. He had to do something,” said Natia Seskuria, a Russia expert and associate fellow at the Royal United Services Institute. “I think today’s statement does not come from the position of strength; it is rather a demonstration of weakness, because I think he feels like he’s under a lot of pressure.”

Western leaders have echoed this sentiment: A European Union official described Putin’s statement as a “dangerous nuclear gamble,” and the US Ambassador to Ukraine Bridget Brink called the referenda and mobilization “signs of weakness, of Russian failure.”

Still, there is still a lot of uncertainty around what Putin’s announcement might mean in this particular phase of the war. Experts questioned how much a partial mobilization might mean in the near-term, even as they cautioned against being too dismissive. Putin has made nuclear threats against the West before, but now he, and the war he launched, is in a much more precarious state.

And then there is how Ukraine, and the West, which is backing Ukraine’s efforts, might respond. So far, the West has condemned Putin’s move, but it isn’t clear how it might affect financial or weapons support for Ukraine.

“There are no easy press the button and you win the war decisions for Putin to take in any circumstances. That is clear,” said Gustav Gressel, senior policy fellow at the European Council on Foreign Relations. “He has basically to choose amongst a lot of possibly negative scenarios, which is the least negative for him. He chose escalation in order to kind of preserve his domestic status and power and prestige, but it’s not guaranteed he’ll get that.”

Putin’s desperation play is still serious

In the last weeks, Russia’s war in Ukraine has entered a new phase.

The Kremlin launched the war in February, with the aim of seizing all of Ukraine and capturing Kyiv. Ukrainian resistance forced Moscow to scale back its ambitious, resetting its focus on the east, in the Donbas, where Russia has fueled a separatist conflict since 2014. Russia and Ukraine engaged in a grinding artillery battle, but Russia also slowly scooped up territory. Advanced Western weapons, though, have helped boost Ukrainian troops, and in September, Kyiv launched a counteroffensive in the Kharkiv region, and has since pushed back Russian forces, town by town.

Russia has now suffered a string of embarrassing defeats, and is seeing mounting casualties more than six months into the war. At the same time, it still controls around 15 percent of Ukraine’s territory. Ukraine’s recent victories, while impressive, are far from driving Russia entirely out.

Putin’s announcement is still likely a direct response to momentum shifting toward Ukraine on the battlefield, and a potential shifting of public sentiment at home against the execution of the war.

But Putin’s announcement on Wednesday still doesn’t offer too many clues on how he will approach this next phase of the war — or what it might mean on the ground.

A partial military mobilization is significant, but for now, it is limited to reservists, and falls short of a full-scale draft. At the same time, Putin’s mobilization decision also prevents most Russian troops from leaving the service or suspending their contracts, a recognition that manpower issues have plagued the performance of Russian forces.

But experts questioned how soon this personnel could make a difference on the ground — or if they might make a difference at all, given the reported low morale among Russian troops and real questions about training and preparedness for these reservists. As Gressel said, just having a lot more manpower isn’t everything; Russia still needs structure, it needs officers, it needs equipment, it needs supply chains.

And then there is a nuclear threat — posed to Ukraine, and, really the rest of the world. Putin has issued nuclear threats against the West before, but, as experts pointed out, this speech contained subtle but potentially alarming shifts in his rhetoric. In his speech, Putin vowed to protect and defend Russia’s territorial integrity, and said he would “use all the means at our disposal” to do so. As experts pointed out, Russia’s nuclear doctrine — that is, its principles about when it would deploy such weapons — has historically rested on the existence of the state, not specifically on territory integrity. “So there’s a bit of uncertainty on how he basically reformulated Russia nuclear deterrence principles,” Gressel said.

This speech, then, may be Putin proposing a much more expansive view of Russia’s nuclear doctrine. That change, if it’s real, could become even more unpredictable when Russia likely illegally annexes swaths of Ukraine. Seskuria pointed out that Putin has repeatedly used nuclear weapons as a threat — at the start of the Ukraine war, but also in 2014. Still, it was a warning, if not about immediate risks, at least about Putin’s commitment to this war. “He’s willing to escalate the conflict to a new level,” Seskuria said. “But I don’t think that the actual prospects for the escalation is that high at the moment.”

For Ukraine, the nuclear threat from Russia is not new. Simon Schlegel, a Ukraine expert with the International Crisis Group, spoke to Vox from Kyiv, where he said he did not see Putin’s announcement as an immediate game-changer, even as officials took Russia’s escalation seriously — and might react by upping their own efforts in their counteroffensive.

“It might even create an incentive on the Ukrainian side to move faster now to put more effort into regaining territory that then the Russians would have more trouble claiming it’s theirs rightfully,” Schlegel said.

But once again, a lot of pressure will fall on the West. Ukraine is dependent on Western financial and weapons support; this counteroffensive, and any chance at retaking and holding territory, depends on Western arsenals. Before Putin’s announcement, some Western partners were reluctant to turn over more advanced weaponry, like German tanks.

Putin, in trying to raise the stakes, is trying to signal to the West that it might be time to back off — “accept that Russia has won at least some territory, and don’t deepen the support for Ukraine.” At least rhetorically, allies and partners have rejected Putin’s threats, but even the United States, with its billions in support to Ukraine, has been careful to avoid provoking Putin. Putin is, of course, hoping that if he escalates, the West will do the opposite. The question for Ukraine’s backers is whether they see this as a real threat, or a bluff from a guy who senses his own victory slipping away — and that is an unpredictable gamble.