Ballistic and Cruise Missile Threat (PDF)
Also maybe you think we should not defend all our military personnel stationed in Europe, or maybe you think we should pull out all our troops and run home with our tails between our legs, either way, such foolish behavior is not in America's strategic interests.
Actually if you read the document is says they could have one, not will. And it's quite a stretch to believe that they can go from missiles with a 1000 mile range to a missile with a 7 or 8 thousand mile range in less than two years.
But again, if Cruz's goal is to push back on Russia by building a missile shield in Europe, and if the purpose really is to protect us from Iran, then why should Putin care if we build it or not?