Donald Trump’s on-again, off-again threats to sanction Russia for its intransigence over peace talks in Ukraine solidified today into concrete action. The US has announced sanctions against Rosneft and Lukoil, two of Russia’s largest oil companies, and their dozens of subsidiaries. Between them, the two giants are responsible for nearly half of Russia’s oil exports – and a serious crackdown on their ability to export crude could deal a serious blow to Russia’s war economy. How serious that blow is depends entirely on how far the White House is prepared to pursue the sanctions. And whether it will cause Putin to cease and desist from his offensive against Ukraine is another question.

The immediate context for Trump’s unexpected move appears to be personal. Over the last week Trump seemed t

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