A group of U.S. Senators are in Ukraine today, attempting to pressure Russian President Vladimir Putin to pull back his "military aggression" against the sovereign nation. 

Arizona Senator John McCain says the U.S. needs to understand the overt power grab by Putin and work to provide assistance to Ukraine. 

The senators are calling the upcoming resolution vote to recognize Ukraine's Crimea as a part of Russia as "illegal and rigged."

U.S. officials expect Crimean voters will choose to become part of Russia.