Vladimir Putin is preparing for a long war in Ukraine, with even victory in the east potentially not ending the conflict, US intelligence has warned.
The warning comes as fierce fighting continues in the east, where Russia is trying to take territory.
Moscow refocused its troops on capturing the Donbas region after Ukraine resisted attempts to take its capital, Kyiv.
But despite this, its forces remain in a stalemate, US intelligence said.
Avril Haines, the director of national intelligence, told a US Senate committee hearing on Tuesday that Mr Putin was still intending "to achieve goals beyond the Donbas", but that he "faces a mismatch between his ambitions and Russia's current conventional military capabilities".
She added that the Russian president was "probably" counting on US and EU support for Ukraine to weaken as inflation, food shortages and energy prices got worse.
However, the Russian president could turn to "more drastic means" as the war continues - although Moscow would only use nuclear weapons if Mr Putin perceived an "existential threat" to Russia.
Defence Intelligence Agency Director Scott Berrier told the same hearing that the Russians and the Ukrainians were "at a bit of a stalemate".
In the latest fighting, Ukraine claims to have recaptured four settlements in the north-eastern Kharkiv region.
Cherkasy Tyshky, Ruski Tyshky, Rubizhne and Bayrak were all snatched back from Russia, Ukraine's armed forces said.
President Volodymyr Zelenskiy said Ukrainian successes were gradually pushing Russian forces out of Kharkiv, which has been bombarded since the war began.
But he said Ukrainians "should not create an atmosphere of excessive moral pressure, where victories are expected weekly and even daily".
Elsewhere in eastern Ukraine:
- In the city of Izyum, the bodies of 44 civilians have been found in the rubble of a collapsed building as the battle for control of the area rages
- The five-storey building collapsed in March as residents hid in the basement from Russian shelling, but rescuers have only just been able to reach the building
- Situated south-east of Kharkiv, Izyum is known as the gateway to Donbas. It is surrounded by forests and rivers, which make it a natural fortress
- The final battle for Mariupol is being fought in the sprawling Azovstal steelworks, where hundreds of Ukrainian fighters are holed up in underground tunnels and bunkers, surrounded by Russian troops
- Capturing Mariupol is a key war aim of Moscow, because doing so would give it control of one of Ukraine's biggest ports and easier access to the wider region
- In the port city of Odesa, missiles struck several buildings overnight and shook homes nearby. One person was killed and five people were injured, Ukraine's armed forces said