SENATOR HILLARY CLINTON is waging two presidential campaigns at once. She is running for the Democratic presidential nomination while keeping a sharp eye on the general election campaign against the Republican presidential nominee, whoever that turns out to be. Senator Clinton wants to run as a centrist, not a liberal, in the general election. But there's a problem. She is being tugged to the left in the nomination fight, forced to take positions that may jeopardize her chances later against the Republican candidate.

Her opponents in the Democratic primaries next year don't have this problem. They are unabashed liberals who have done nothing to place themselves near the ideological center of American politics. Clinton, however, spent her first term as senator from New York downplaying her image as a staunch liberal. Instead, she has sought with some success to fashion a reputation as a centrist on some several key issues, particularly national security. And while doing so, she became the undisputed frontrunner for the 2008 Democratic nomination. She became electable.

A glance at the breakdown of red and blue states in the 2004 presidential race shows how little it would take for her to win the general election. If she holds the states won by Democrat John Kerry, she would need to add only one populous red state or two smaller ones. And there are numerous Republican states that have drifted toward the Democrats since 2004--Ohio, Colorado, Iowa, Montana, Nevada, Arizona, and Virginia, just to name a few.

But Clinton's ability to pick up one or two of these red states depends on her maintaining credibility as a centrist on key issues. That is a difficult task. Given the pressure from her party's liberal base and from her Democratic opponents for the presidential nomination, it's now very much in doubt whether she can accomplish it. She's already becoming more liberal than it's safe to be in a presidential election in a nation with an enduring center-right majority.

As surprising as this may sound, Clinton starts her campaign as the Democratic candidate furthest to the right. The only two Democrats who might have gotten to her right--Sen. Evan Bayh of Indiana and former Gov. Mark Warner of Virginia--dropped out of the race. So she faces competition from a phalanx of liberals, two of whom--Sen. Barack Obama of Illinois and former Democratic vice presidential candidate John Edwards--are formidable opponents.

In her six years in the Senate, Clinton has gone a good ways toward achieving the threshold requirement for a female candidate for president: making herself believable as a commander in chief. She did this by spending long hours at Senate Armed Services Committee hearings, forging a supportive relationship with Donald Rumsfeld, and voting in 2002 to authorize the invasion of Iraq.

She became conversant on defense issues. At a breakfast with reporters in late 2003, I asked her if there had been good reason to believe, as President Bush did, that Saddam Hussein had weapons of mass destruction. "The intelligence from Bush 1 to Clinton to Bush 2 was consistent," she said, in concluding Saddam had chemical and biological weapons and was developing nuclear weapons.