This morning on "This Week," Sen. Chris Murphy, D-Conn., told ABC's George Stephanopoulos there was nothing the U.S. could do militarily to prevent Russia from moving into Eastern Ukraine following its seizure of the Crimean Peninsula. But Murphy advocated for new sanctions on Russia that could put economic pressure on President Vladimir Putin and prevent further Russian action in Ukraine.

"Clearly, this is a longer-term effort to build up the Ukrainian military," said Murphy. "But if on Monday, we announce - with the European Union - a set of crippling sanctions coming after not only individuals, but Russian business entities, I think that sends a strong message to Putin."

"I think [Putin] marched into Crimea because he didn't believe that the United States and Europe would actually take a chunk of flesh out of his economy," Murphy added. "And, if we stand together on Monday, that gives us a chance, at least, to change the calculus in Moscow."

When asked about the effectiveness of economic sanctions, Murphy said, "We have to wait for our European friends to tell us if they're willing to move forward… There is no doubt that if you cut off Russian gas to Europe, it will hurt. There's no doubt that if you freeze Russian assets in places like Germany and Great Britain, it will hurt them."

"But this is a threat to the territorial integrity of Europe - who knows who's next?" he added.

Murphy also expressed doubts about the legitimacy of today's referendum on whether Crimea should remain part of Ukraine or join Russia.

"This sham referendum isn't fooling anyone," he said. "The Ukrainians are not going to go down without a fight. If Russia really does decide to move beyond Crimea, it is going to be bloody and the fight may be long."

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