Opposing the Libyan intervention and by extension, President Obama, is relatively easy for a party finding its way in a war-weary election. The bigger challenges by far are Afghanistan, and Iraq, and U.S. troops stationed in seeming perpetuity in Europe and South Korea. Where will they draw the line, and will Democrats join them? In an election defined by partisanship, this may be the place where the right and left come together — or switch places.