US sees signs Russia is 'struggling,' has warned of catastrophe if Putin uses nuclear weapon: Sullivan

The U.S. is seeing evidence that Russia is "struggling" in its invasion of Ukraine and has warned Moscow that there would be "catastrophic consequences" if it were to use a nuclear weapon in its war against Kyiv, the White House national security adviser said Sunday.

Jake Sullivan, in an interview with ABC "This Week" anchor George Stephanopoulos, pointed both to the protests against Russian President Vladimir Putin's mobilization of 300,000 reservists and to what Sullivan called "sham" annexation referendums in Russian-controlled areas of Ukraine.

"These are definitely not signs of strength or confidence. Quite the opposite: They're signs that Russia and Putin are struggling badly," Sullivan said while noting Putin's autocratic hold on the country made it hard to make definitive assessments from the outside.

"It will be the Russian people, ultimately, who make the determination about how Russia proceeds and the extent to which that there is resistance and pushback to what Vladimir Putin has tried to do, calling up these hundreds of thousands of young men," Sullivan added.

"Do you want them to rise up and replace Putin?" Stephanopoulos asked.

"At the end of the day, the future of Russian politics is going to be dictated, not by Washington, not by anyone in Europe, but by the people inside Russia," Sullivan responded. "And what you are seeing in the streets right now is a deep unhappiness with what Putin is doing."

His comments come amid escalating rhetoric from Putin as Russian forces have been forced to cede large swaths of northeast Ukraine while retreating from a Ukrainian counteroffensive this month.

Last week, Putin called up reservists and suggested that tactical nuclear weapons could be used to change the course of the war, groundlessly accusing the West of threatening Russia's territorial integrity. Since before attacking Ukraine in February, Putin has cast the invasion as a matter of Russian national security.

"The territorial integrity of our homeland, our independence and freedom will be ensured, I will emphasize this again, with all the means at our disposal. And those who try to blackmail us with nuclear weapons should know that the prevailing winds can turn in their direction," Putin said in a speech last week.

"I want to remind you that our country also has various means of destruction, and some components are more modern than those of the NATO countries," Putin added.

On "This Week," Sullivan declined to explain precisely what warnings have been communicated between Russia and the U.S. but he said that there would be dire repercussions if such a weapon were used.

"We have communicated directly, privately, to the Russians at very high levels that there will be catastrophic consequences for Russia if they use nuclear weapons in Ukraine. We have been clear with them and emphatic with them that the United States will respond decisively alongside our allies and partners," Sullivan said.

"So that means taking the fight directly to Russia?" Stephanopoulos asked.

Sullivan demurred: "We've been careful in how we talk about this publicly because, from our perspective, we want to lay down the principle that there would be catastrophic consequences but not engage in a game of rhetorical tit-for-tat."

Stephanopoulos also asked Sullivan if protests in Iran over the death of a woman who was not adhering to the country's strict female dress code would be enough to topple the government in Tehran.

"The United States ... hasn't necessarily over many decades had a great track record of perfectly predicting when protests turn into political change, and I can't perfectly predict that sitting here today. What I can say is they do reflect a deep-seated and widespread belief among the population of Iran, the citizens abroad, the women of Iran, that they deserve their dignity and their rights," Sullivan said.

Stephanopoulos pressed, given the Iranian government's actions, if the Biden administration should continue seeking to revive the Obama-era nuclear deal which President Donald Trump scrapped. Conservatives have repeatedly criticized those efforts.

Sullivan said that the White House feels diplomacy and political pressure can go hand-in-hand.

"The fact that we are in nuclear talks is in no way slowing us down from speaking out and acting on behalf of the people of Iran," he said. "We're not going to slow down one inch in our defense and advocacy for the rights of the women and citizens of Iran."