Voters in the semi-autonomous Crimean region Sunday decided whether to secede from Ukraine and rejoin Russia. RIA Novosti reported the referendum was approved by 93 percent of voters queried in exit polls. Russian troops have been stationed in Crimea since the region reached out to Russia for help deterring anti-government protesters.
"Well, I think economic sanctions are a very important step," McCain said. "Identify these kleptocrats and -- look, Russia is a gas station masquerading as a country. Its kleptocracy, its corruption, it's a nation that's really only dependent upon oil and gas for their economy. And so economic sanctions are important."
McCain also said some military assistance would help Ukrainians.
"Get some military assistance to Ukrainians, at least so they can defend themselves. Resume the missile defense system in Poland and the Czech Republic. Look at Moldavia and Georgia, both of whom are occupied by Russian troops as we speak, a path towards membership in NATO," he said.
However, McCain added that he doesn't think the U.S. should send troops to Ukraine.
"Look, that doesn't mean American boots on the ground, although maybe delivering some humanitarian supplies by U.S. aircraft, military aircraft, in Kiev might have a kind of beneficial effect," McCain said.
Meanwhile, Durbin told NBC's "Meet the Press" sanctions are the best international response to Russia's invading Crimea.
"They invaded a sovereign nation. If we're going to stand by and let them do to Ukraine what they've done to Georgia, the Republic of Georgia, then you know, you can expect more," Durbin said.
Flake agreed, telling "Meet the Press": "Well, certainly we've got to move in hard now with sanctions. Regardless of whether they move tomorrow or the next week or hold back. We're going to move forward with sanctions, not just us but our European allies, as well."