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(CNN) – Russian President Vladimir Putin has yet to acknowledge the forces in Ukraine's Crimea peninsula are even Russian, but a commander of troops – who are wearing Russian uniforms without identifying insignia and driving vehicles bearing Russian plates – was frank. He told CNN he came from a Russian city near Crimea and had been dispatched by his commanding officer from Sevastopol to a ferry port on the eastern side of the Crimean peninsula.
Conservatives are saying President Barack Obama is partly to blame for Putin's bold moves.
"We have created a leadership vacuum in the world, and it is filled by the Putins in the world, by people without our values or our interest. And it's to the detriment of the United States and our friends and allies around the world. It is the United States that's injected that instability into the world equation,” former Defense Secretary Donald Rumsefeld told Fox News.
But Democratic Senator Robert Menendez, chairman of the Senat Foreign Relations Committee, said the blame lies solely on Putin's shoulders.
"He has created the uncertainty in the world. It's his own version of Russian roulette. The only thing this time (is) the gun is aimed at the international community's head, and that's why there has to be a forceful response," Menendez said in an interview with CNN's "The Lead with Jake Tapper."
"Putin has violated his international agreements here, and a wide range of them, and ultimately shown that he is pursing his vision of adding to the Russian federation by force," Menendez said.
Last September, when Putin wrote an op-ed in The New York Times chastising American involvement in Syria, Menendez said the Russian leader's words almost made him sick.
Now, Menendez says Putin should take his own advice.
"I would say now, listen to your own words. Basically, what President Putin was saying to an American audience about Syria is that we have to stop using the language of force, and proceed ... on the path of civilized diplomatic and political settlement," said Menendez.
For more of our interview with Sen. Robert Menendez, check out the video above.