As U.S. and European officials threaten sanctions in their face-off with Russia over Ukraine, Vladimir Putin’s $160 billion in oil and natural gas exports may be his most potent weapon to limit punitive measures. The U.S. and its European allies, set to meet today in Brussels, have few levers to deter Putin even as they warn Russia not to annex Crimea after a referendum in Ukraine’s southern region yesterday. Threats of visa bans and asset freezes haven’t rattled the Kremlin thus far. Russia, the world’s largest oil producer, exported $160 billion worth of crude, fuels and gas-based industrial feedstocks to Europe ... (full story)