Pfeiffer said everything that Russia has done in Crimea has been a violation of international law and bad for stability in the region.
"President Putin has a choice about what he's going to do here. Is he going to continue to further isolate himself, further hurt his economy, further diminish Russian influence in the world, or is he going to do the right thing?" Pfeiffer said on NBC's "Meet the Press."
Members of Congress said they were prepared to enact tough sanctions on various Russian leaders. It's also considering action to help the Ukrainian economy, but $1 billion in loan guarantees is on hold because Congress is on a break.
"President Putin has started a game of Russian roulette and I think the United States and the West have to be very clear in their response because he will calculate about how far he can go," said Sen. Robert Menendez, the Democratic chairman of the Senate Foreign Relations Committee.
Menendez appeared on Fox News Sunday along with the ranking Republican on the Foreign Relations Committee, Sen. Bob Corker of Tennessee. Corker said the U.S. and Europe were entering a "defining moment" in their relationship with Russia.
"Putin will continue to do this. He did it in Georgia a few years ago. He's moved into Crimea and he will move into other places unless we show that long-term resolve."
Democratic Sen. Chris Murphy of Connecticut returned early Sunday from meetings in Ukraine. He called an annexation vote taking place in Crimea a "sham referendum." He said that Ukrainians he talked to, both inside the government and outside, said war could occur if Russia attempts to annex more territory. They indicated that "If Russia really does decide to move beyond Crimea it's going to be bloody and the fight may be long," he said on ABC's "This Week."
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