McCain also conceded that at this point, Crimea belong to Russia.
"It's a done deal," he said about Crimea's referendum to join Russia."You can’t say that there’s anything but a fait accompli."
That doesn't mean that the U.S. should give up, however, he added.
McCain listed a few of the U.S. options that could help Ukraine eventually regain Crimea, including some military assistance to Ukraine and economic sanctions against Russia.
He said that the U.S. needs a "fundamental reassessment of our relationship with Vladimir Putin."