We keep seeing article after article and tweet after tweet about Putin using tactical nukes in Ukraine. If he does that then he's the dumbest individual ever. There's just zero upside for him.
First, it makes no tactical sense. There are no troop concentrations significant enough for a tactical nuke to turn the tide of the war. It would likely just enrage Ukraine and make them less willing to negotiate. Additionally, Russian troops are not in any shape to navigate a nuclear battlefield. So he'd probably end up killing as many of his men as he would Ukrainians. Then there's the fact that it invites reprisals from the west. If the west started airstrikes in Ukraine, Russian forces would be pushed out of Ukraine incredibly quickly.
Next, it makes no political sense. There's an idea that dropping a nuke on Ukraine might scare the west and cause them to force Ukraine to seek peace. While that's possible, it's a long shot. It's more likely the west retaliates and drives Russia out of Ukraine. More importantly it would likely close virtually every market for Russian products. China and India aren't terribly pleased with the war as is. This would be a red line that would very likely cause them to cut off trade with Russia. Without supplies from China and without those markets to sell its oil, Russia's economy's lifespan would be measured in terms of weeks.
Then there's the fact that it's an enormous personal risk for Putin. If he orders a nuclear strike there's a very real chance it instigates a military coup. If the military turns on Putin and refuses to obey the order, he's done. He'd be arrested or just killed. If he's arrested I think there's a good chance the general that takes power hands him over to the Hague to smooth over relations with the West and get sanctions eased. If the order is followed, it could easily spark massive civil unrest. People aren't happy with the mobilization, playing around with nukes is downright terrifying. It's one of the things that could incite a revolution.
However, threatening nukes and perhaps even some kind of demonstration (e.g. test close to the Ukraine border) gets most of the benefit of using nukes without a lot of the nasty consequences. I don't see a demonstration without any actual impact provoking the west into action. I think that would be acceptable to China and India as well. It would also have a good bit of the intimidation factor actual use of one would have.
We've seen Putin use nuclear threats to great effect in the past. It's a regular part of his playbook. And the threats are likely doing their intended purpose currently. It has the West on edge which will likely further drive cracks in the unity of supporting Ukraine. Americans go to the polls next month and the more concerned they are about Ukraine the more likely they'll be to vote for doves who could really hamper Biden's ability to supply Ukraine. We also see Europe already on edge staring down an energy crisis. This just makes even more people want to be done with the Ukraine war and return to greater stability.
Finally, Putin doesn't need nukes to win. At least not yet. The partial mobilization has caused a big public opinion hit for Putin. He delayed doing it as long as possible for this reason. If his plan is to nuke Ukraine into submission, there's no reason to call up reserves. Why piss off your country, arm a large number of your people, then use nuclear weapons making you even more unpopular? No, the partial mobilization makes sense. The Ukraine offensive has taken its toll on Ukrainian forces. We're starting to see reports of exhaustion and times where there are no reserves to take advantage of a situation. How much gas is left in the tank is a real question. Then once the winter sets in, it will make advances by either side very difficult.
By the time spring rolls around, Russia will have hundreds of thousands of new troops trained up and deployed. I think Putin has a spring offensive in mind. Add in a cold winter causing more fracturing of European unity and the West's diminishing ability to supply Ukraine, it could be an opportune time.
Using a nuke in Ukraine would make a loss there very likely. Biding time, letting the west's support wane, and waiting for reinforcements gives a pretty high chance of achieving goals without pissing off China and India.