Like it or hate it, policymakers in Washington are still obsessed with the deficit. That’s why think tanks keep churning out clever plans to cut spending and raise taxes.And here’s a new paper from the Council on Foreign Relations offering an interesting twist on the theme. Using economic modeling, Michael Levi and Citgroup’s Daniel Ahn suggest that a tax on oil consumption could be one of the least harmful ways to trim the budget deficit.How do they figure? Levi and Ahn first assume that Congress will enact a big deficit-reduction package over the next 10 years that includes about $3 in spending cuts for every $1 in corporate and income tax