• Russia's latest attacks on Ukraine aren't a show of strength, but a "show of weakness" that reflects its inability to advance and seize Ukrainian territory, said Kurt Volker, a distinguished fellow at the Center for European Policy Analysis.
• "Putin's goal was to take over Ukraine, replace the government, have someone in Ukraine that was subordinate to Moscow. That's simply not going to happen," the former U.S. ambassador to NATO told CNBC's "Capital Connection" on Tuesday.
• "He's not actually able to affect the course of the war anymore," he added.

Russia's latest attacks on Ukraine aren't a show of strength, but a "show of weakness" that reflects its inability to advance and seize Ukrainian territory, said Kurt Volker, a distinguished fellow at the Center for European Policy Analysis.

On Monday, Russian President Vladimir Putin confirmed that he ordered long-range missile strikes on a number of locations in Ukraine targeting military, energy and communications facilities.

"Putin's goal was to take over Ukraine, replace the government, have someone in Ukraine that was subordinate to Moscow. That's simply not going to happen," the former U.S. ambassador to NATO (2008-2009) told CNBC's "Capital Connection" on Tuesday. "Ukrainians have made tremendous inroads taking territory back. This is the kind of thing that Putin has to resort to."

"He's not actually able to affect the course of the war anymore."

Volker, who was also U.S. special representative for Ukraine negotiations (2017-2019), added that Russia's increasing aggression is an expected reaction to Ukraine's resistance.

Last Saturday, an explosion obliterated part of the bridge linking the Russian mainland to Crimea, which Moscow illegally annexed in 2014, in what appeared to be a strategic move to disrupt a key supply route for Russian troops.

Though Kyiv has not claimed responsibility for the attack, Volker said "we have to assume they were behind it."

"We are going to see continued efforts by the Ukrainians to make sure that Russian forces deployed in Ukraine are unable to sustain themselves, and that they have a very difficult winter ... This lays the conditions for Ukraine to take back its territory later this year, and more next year."

The West needs to do "a lot more" to help Ukraine with their defenses to these unpredictable attacks and end the war more quickly, he added.

Nuclear weapons

Putin's explicit threats to use nuclear weapons have called into question the risk of an impending nuclear conflict.

Volker said the possibility of Putin using nuclear weapons can never be ruled out, but he will have more to lose than gain.

"It does not serve any military objective that Putin has to use nuclear weapons. It will actually make the territory he's attacking uninhabitable ... and blow back on his own forces in ways that will weaken his own military capabilities."

Others have taken a similar view. Retired Lieutenant General Ben Hodges, former commanding general for the U.S. Army in Europe, told CNBC earlier this month that although the nuclear threat is "absolutely a credible" one because Russia has thousands of nuclear weapons, it's unlikely that Putin will resort to it given the lack of a battlefield advantage.

Volker added that even the Russian military may not support Putin should he call for nuclear weapons to be deployed.

"The Russian military knows full well that crossing the nuclear threshold is a big deal for the West and other nuclear powers, including China. I have no doubt that it would draw a direct response against Russian military, which they certainly don't want."

"Would they even follow an order, if given that order by Putin? And would Putin give such an order, if he's concerned about the reliability of his military?"