Putin is not worried about what Obama thinks or the U.S. he will do whatever he wants.
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President Obama told Russian President Vladimir Putin in a 90 minute phone call on Saturday that his country sending troops into Ukraine is a “clear violation” of that country’s sovereignty, according to the White House.

But a defiant-sounding statement issued later by the Kremlin in Moscow said Putin stressed to Obama that the situation in Ukraine poses “real threats” to the life and health of Russian citizens and compatriots who live in Ukrainian territory.

“Vladimir Putin emphasized that, in the case of a further spread in violence in eastern regions (of Ukraine) and Crimea, Russia maintains the right to protect its interests and the Russian-speaking population that lives there,” the Kremlin statement said.