WASHINGTON -- Note it in the history books: In the month of October, in the year 2007, the American political battlefield was reshaped. A die was cast, a donnybrook begun. Old agreements were broken, new alliances formed. And one powerful political force appeared solitary on the horizon, as magnetic and polarizing as anything this nation has ever seen. With Tuesday's debate in Philadelphia, the era of Hillary Clinton officially arrived.

Now we as a nation must deal with it. For the next two months, in the clumsy holiday stumble toward the Jan. 3 Iowa caucuses, the specter of Clinton is destined to overwhelm the nation's news broadcasts, the pundit round tables and the cluttered debates. For both Republicans and Democrats, she will lurk behind all discussions, testing the willpower and endurance of the American people. The hatred she can summon, the hope she can inspire, all of it, will be on display day after day. And no matter how they feel about her, voters will be forced to endure sense memories of the '90s, flashing back to that era's exhausting fog of anti-Clinton rhetoric.

Wonks and political scribes have seen this coming for months. There have been many story lines so far in the 2008 campaign: the rise of Barack Obama, the re-creation of Mitt Romney, the collapse and resurgence of John McCain, the legitimization of Rudy Giuliani as a Republican contender. But in a way, these were all just diversions from the main plotline: Can anyone -- Democrat or Republican -- stop Clinton? And can anyone, besides faithful Hillary supporters, deal with the Hillary fatigue to come?

For Republicans, another Clinton's candidacy was always a blessing in disguise. They knew her as a masterful politician, a policy expert, a formidable foe. And a gift. No one could unify the despondent GOP rank and file as well. Seven years of George W. Bush has infected the conservative movement with confusion and despondency. Clinton was the antidote, a savior to be championed. Months ago, Karl Rove raced through the city streets, singing her name. Clinton is coming, he cheered. Clinton is coming. The Republican candidates followed suit, calling her out on the trail: a socialist, a big spender, liberalism incarnate.

"By showing that Governor Romney is the perfect Republican antidote to the Hillary Clinton affliction, as a campaign we can show that he's the best Republican for this nomination," explains Romney spokesman Kevin Madden. All the major Republican candidates think the same way. Rudy Giuliani has built his campaign around her. On Wednesday, the McCain campaign sent out its latest fundraising appeal, a newspaper mockup that blared from the hypothetical future: "McCAIN DEFEATS CLINTON: McCain's Straight Talk Wins Historic Victory Over Hillary Clinton." He knows this is the message that opens pocketbooks.

For Democrats, the gentlewoman from New York by way of Arkansas was initially a more neutral and ambiguous force. She offered a glimpse of the heady days of 1992, when there was new hope from Hope. Her smarts, her poise, her classy laugh, won her early plaudits and praise. But she soon became a victim of her own success, her own precise caution. She sucked all the air out of the room. In a primary field crowded with talent and money, she scored near 50 percent of the Democratic vote in early national polls. She became the runaway front-runner.

This left her well-heeled opponents no other choice. John Edwards hired the populist firebrand Joe Trippi and retooled his war on poverty as a war on Hillary. Hassled by his fundraisers, Barack Obama sent out his minions with a new fighting message and then sat down with the sages of the New York Times. I will attack her, he vowed. I will defeat her. The cable-news talking heads rejoiced. Blood in the water, they assured us. Blood in the water, at last. (Would the ratings bump follow?)

It will be like this from now on: "The race for the nomination itself appears to be Hillary Clinton's to lose," pundits like MSNBC's Tucker Carlson will say over and over again, as he did on Tuesday. "In a moment, we'll identify the ways by which Mrs. Clinton could, in fact, lose." (Salon also identified them, though without Carlson's palpable glee.)

At Tuesday's debate, she did not disappoint. She faltered under the pressure. She hesitated on a question about giving driver's licenses to illegal immigrants. She tried to answer both ways. She also tried to pull one over on NBC's Tim Russert, saying that her archival records from the Bill Clinton White House would be released in due course. Not true, said Russert, showing the letter her husband had signed forbidding their release. She stammered some more. Obama closed for the kill. "This is not turning the page," he said. Meaning, I will turn the page.

Edwards also shone in the debate, easily slighting Clinton at each turn. His campaign put out a press release Thursday. "On Tuesday night millions of Americans saw John Edwards speak honestly and directly, while Senator Clinton once again took multiple positions on multiple issues," it read. "We understand that the Clinton campaign isn't happy about that, but instead of smoke and mirrors, how about some truth-telling?"

And so, as if by circumstance, the candidates from the left and the right have come to an unspoken agreement. There is a common opponent, a single woman who stands in their way. Clinton has become the master narrative, the reason for being. She is not everything. The Republicans will still attack each other in the coming weeks, while the Democrats still talk about the horrors of the Bush years. But she will still be there in the background, hidden in every crowd, every stump speech, every rally, like Waldo. Everyone who does not support her will be willing her defeat. As Wolf Blitzer, CNN's understater of the obvious, put it Wednesday, "Sen. Clinton may be feeling like a punching bag of sorts."

And it is in this environment that Clinton will rise to the challenge. She always knew it was coming, this curse of the Clinton name. She has handled it before. She will try to handle it again. "Personally, I have taken a lot of attacks over 15 years," Clinton said a few weeks back, in a New Hampshire apple orchard. "That's fine. I can protect myself. I can survive. It doesn't really bother me anymore."

This time, however, the challenge is greater. It will not be enough to protect herself. Amid all the fury and fireworks, she must convince Democratic voters in Iowa, New Hampshire, Nevada, South Carolina and the nation that she is worth all the trouble, all the backbiting, the claims and counterclaims that she cannot control. She must convince American liberals that her talents outweigh the hatred she can summon. Then if she wins the nomination, she must persuade the rest of the country to ignore all the animosity Republicans are sure to drum up. She must ask the nation to judge her on her merits. It's a titanic task for a larger-than-life politician, a battle for the ages.

Hillary Clinton has prepared for this moment all of her life. She stands, alone and determined. And the world watches, waiting to see what happens next.