Sen. Ben Cardin (D-Md.) said on Sunday that the armed rebellion from the Wagner Group shows Russian President Vladimir Putin’s power is waning among his people.

In an interview with Shannon Bream on “Fox News Sunday,” Cardin pointed to the rebellion by Yevgeny Prigozhin’s Wagner Group as evidence of Putin’s declining credibility, even among his longtime allies.

“Putin has lost his credibility with his own people. His account of why he went into Ukraine is now being challenged, I think, with public opinion and Russia itself,” Cardin told Bream.

Prigozhin is the owner of the Wagner Group, which is a Kremlin-aligned private army of mercenaries and inmate recruits that has led some of Russia’s most brutal battles in Ukraine. Prigozhin is a longtime Putin ally and has benefited from the relationship in a variety of ways.

On Friday, however, Prigozhin escalated his criticism of Putin’s war in Ukraine and called for the ouster of Russia’s defense minister, Sergei Shoigu. Prigozhin-led Wagner Group fighters left Ukraine, where they had been fighting, and crossed into Russia. Despite Prigozhin’s pledge to “destroy anyone who stands in our way,” an agreement was ultimately reached with Belarus and Prigozhin ordered his troops to stop the advance.

In recent months, Prigozhin’s criticism of Russia’s war has also been escalating. On Friday, he released a viral video that denounced Putin’s explanation of the war as false and accused Russian oligarchs of being responsible for the war. In a subsequent video, he also accused the Russian military of attacking his group’s campsite and killing many of his fighters.

“The war was not needed to return our Russian citizens and not to demilitarize and denazify Ukraine,” Prigozhin said in the initial video. “The war was needed by oligarchs. It was needed by the clan that is today practically ruling in Russia.”

The Russian Defense Ministry has denied these claims, and the National Anti-Terrorism Committee opened a criminal case into Prigozhin hours after he posted the video.