It's easy to see why conservatives would be salivating at the thought of a Hillary primary challenge. Presidents who face serious primary challenges—Ford, Carter, Bush I—almost always lose. The last president who lost reelection without a serious primary challenge, by contrast, was Herbert Hoover. But in truth, the chances that Obama will face a primary challenge are vanishingly slim, and the chances that he will lose reelection only slightly higher. No wonder conservatives are fantasizing about Hillary Clinton taking down Barack Obama. If she doesn't, it's unlikely they will.