Rand Paul has joined  the “punish Russia” chorus:
It is important that Russia becomes economically isolated [bold mine-DL] until all its forces are removed from Crimea and Putin pledges to act in accordance with the international standards of behavior that respect the rights of free people everywhere.
Sen. Paul makes several proposals in his article, most of which seem unworkable or irrelevant, but this is the one that has the least chance of succeeding on its own terms. Russia has the eighth-largest  GDP in the world. Even if it were somehow politically possible to get all of its major trading partners to agree to “isolate” it, it would be economically ruinous for many of them to do so. No matter how assertive or bold the U.S. might be, there is no real chance that Russia will be isolated economically, and even less drastic punitive measures could have very undesirable effects .
Paul Pillar observed  recently that the costs and consequences of sanctions are often overlooked in these debates:change_me
The multiple drawbacks and limitations of economic sanctions are too infrequently considered before sanctions are enacted. These include issues of who exactly in the target country will be hurt, and who might actually benefit. They also include consideration of counterproductive political reactions, including resistance to be seen buckling under pressure [bold mine-DL].
The costs, including economic costs, to ourselves of sanctions we impose are insufficiently acknowledged. In some situations trade patterns are such that the costs to ourselves may be minimal, but in those circumstances, and for that very reason, the desired impact on the target country is likely to be minimal as well. This may be the case with Russia today, with which the European Union has much more trade than the United States. Unilateral U.S. sanctions are thus likely to be ineffective with regard to Russia, while being needlessly disruptive to cooperation and common purpose with regard to the Europeans.
If the situations were reversed and a number of foreign governments sought to use economic sanctions to compel the U.S. to withdraw from territory that it had invaded, we can be reasonably sure that our leaders would react very badly to the attempt. Even if those leaders could be persuaded that they had erred by invading, they would be reluctant to give in to foreign pressure and could easily become even more intransigent in the face of such pressure. If there were no recognition of error, and our leaders believed that they were in the right to act as they did, they would be even more likely to respond to sanctions with punitive measures of their own. Sanctions are generally useless in achieving anything desirable, but they are frequently not harmless, and they can make the targeted regime even more determined to persist in the course of action that prompted them. While it may be satisfying and politically convenient to impose sanctions as a punishment, it usually doesn’t produce in the change in behavior that the U.S. wants, and it could very well contribute to a dangerous increase in tensions that will make the larger crisis harder to resolve.