Vladimir Putin
Putin said during a visit to a military hospital that Russia was going to intensify its attacks on Ukraine. AFP

Former US President George W. Bush believed he had a "sense of his soul". British ex-premier Tony Blair thought he deserved a place at the "top table". And French President Emmanuel Macron invited him for hours of talks at his official holiday residence.

For much of President Vladimir Putin's two-and-a-half decades in power, Western leaders thought they understood the strategy of the Kremlin leader and argued that Russia merited a place as an international partner.

But that approach was blown apart two years ago on February 24, 2022, when Putin ordered the invasion of Ukraine, consigning to a distant past images such as that of the smiling Russian leader bounding up the steps of Macron's Mediterranean Fort de Bregancon residence in August 2019 bearing flowers for the French leader's wife Brigitte.

While Putin failed in his initial aim of taking key Ukrainian cities in a lightning offensive that first winter, he now appears increasingly content, seeing off Ukraine's much-anticipated summer 2023 counter-offensive and controlling key territories in the south and east of the country.

In a symbolic gain for Moscow, the eastern Ukrainian town of Avdiivka fell to Russian troops last week after months of battle.

And in a devastating blow to the Russian opposition, Putin's top critic Alexei Navalny died in his Arctic prison last week. His team says he was murdered.

"It's true to say that President Putin is confident that he can outlast the West and so it's incumbent on us to show the resolve to prove him wrong," said a senior Western official, asking not to be named.

Putin had made increasingly bullish statements, declaring in December that Ukraine "does not have a future" and -- in a recent interview with controversial right-wing US talk show host Tucker Carlson -- that a strategic defeat of Russia is "impossible by definition".

Western leaders have responded by insisting that defeating Russia in its war on Ukraine is the only option, with Macron declaring last month that Europe's priority must be to "not let Russia win".

Analysts say only drastically ramped up Western support for Ukraine as it runs out of munitions can change the momentum.

But even this is far from certain, as US legislators hesitate over a new aid package, Putin awaits a possible Donald Trump victory in this year's US presidential election and cracks emerge in Europe.

"It is a race by both sides to rebuild their offensive capacity," said Andrea Kendall-Taylor, senior fellow at the Washington-based Center for New American Security (CNAS).

"If the Western funding does not come through, if Russia gains some sort of advantage, then they have the possibility of making some more gains," she said.

"The momentum has shifted."

Kendall-Taylor added that if Ukraine can hold its lines in 2024, it could pressure Russia more in 2025 if new resources come through.

"From Putin's perspective, 2024 is quite critical," she said.

Ukraine is deeply unsettled by the prospect of a return to the White House of Trump, who famously declared in 2023 he would "have that war settled in one day, 24 hours" if elected again.

Far-right parties, which commentators fear would advocate a softer line against Russia, are on the rise in France and Germany.

Tatiana Stanovaya, founder of the R. Politik consultancy, said Putin saw 2024 as a "window of opportunity" to turn the course of the war in Russia's favour, partly due to the weaknesses in the West.

"He anticipates a temporary gap in Western military support, with ammunition production expected to ramp up only by early 2025," she said.

"The US election cycle might lead to a less decisive American geopolitical strategy towards supporting Kyiv, and the European Union, facing its own internal disagreements, is unlikely to compensate for this support on its own."

But one reason for some optimism in the West may come from Russia's own domestic weaknesses.

Its economy is firmly on a war footing, there are signs of public fatigue with the duration of the conflict and it has suffered astronomical losses.

So far, Western sources say 350,000 soldiers have been killed or wounded on the Russian side.

The Western official said there were things which "really ought to be a cause for concern" for Putin, with government spending on defence and security "storing up some real long-term problems in the Russian economy".

"Balancing the domestic stability picture absorbs a large percentage of Putin's bandwidth," said Dara Massicot, senior fellow at the Carnegie Endowment for International Peace, noting "overconfidence" in the current tone of Russian officials.

But without significant Western support "I don't know what kind of negotiating position the Ukrainians would be in. It would be a terrible one," she said.