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A year ago, when the administration of U.S. President Barack Obama initiated its “reset” of U.S.-Russian relations, two things were clear: First, the U.S. Congress, particularly the Senate, would have an outsized role to play in the process; and, second, the Democrats would likely have a fillibuster-proof 60 votes in the Senate, making the advancement of Obama’s major Russia policy overtures a bit easier than might otherwise be the case. A year later, the first proposition remains true, but Republican Scott Brown’s recent upset victory in the Massachusetts Senate race complicates the second since Democrats no longer have 60 seats in the Senate— the threshold that allows a party to pass...