(CNN) -- Unable either to win the war in Ukraine by proxy or to retreat from the conflict because of the enormous blow a defeat would deliver to his regime's legitimacy, Russian President Vladimir Putin appears to be sending in regular troops to attack Ukraine. The action is south of rebel-held Donetsk, which, until Russia's heightened involvement this week, was on the verge of being retaken by the Ukrainian army. It is likely that in response to Russia's escalation, the United States and European Union will contemplate more sanctions. The problem is that all the relatively "painless" economic measures have already been taken. So both the U.S. and Europe are now left looking at actions that will hurt their own industries and financial institutions.
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Leon Aron: Unable to win by proxy or to retreat in Ukraine, it appears Putin sent troops
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He says U.S., Europe mulling sanctions, but only ones left will also hurt own financial interests
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He says West can help Ukraine win by sending support like radar jamming technology
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Aron: If Russia sees casualties, Russian patriotic support for Putin, and war, will drop
Sending guns and bullets is not necessary -- @placeholder has enough.