She could, as she once said, have stayed home and baked cookies. Instead, Hillary Clinton has devoted her every waking minute for the past nine years to the pursuit of power that she genuinely believes she could use to the public good. Her fellow Democratic grandees are now steeling themselves to tell her to drop her bid for the presidential nomination - and drop it she must. Yet the paradox of her position is that this leaves her closer to real power than she has ever been.

For five months it has been said that both major candidates in this race, if victorious, would transform America's political landscape simply by virtue of their race or gender. The truth is that Mrs Clinton has transformed it already. By making the transition from political spouse to political candidate she became unique among First Ladies. By proving herself not just electable despite the ridicule heaped on her during the Lewinsky affair, but a front-runner in her first tilt at the White House, she has made herself unique among American female politicians. She has shown that gender is no bar to informal power in Washington, where she has few rivals in the art of political cajolery. She has demolished the myth that Americans could never elect a woman president, building a campaign machine that looked unbeatable until ambushed by Barack Obama. And she has out-toughed her every male rival, including Mr Obama.

That toughness, carefully hidden, brought Mrs Clinton from the nadir of her failed healthcare reforms in 1994 to the apparent status of nominee-in-waiting 13 years later. The same toughness, out in the open, has won her endless curtain calls from loyalists in her contest with Mr Obama. But it may also be her undoing. Hoping for a resurrection like those trademarked by her husband, she has instead dragged out this race at the risk of permanent damage to the Clinton brand.

Her determination has fatally clouded her judgment. For many the last straw was her mention last week of the assassination of Robert Kennedy late in his nomination bid in 1968, apparently to justify her own refusal to concede. The impression that she was clinging on in case Mr Obama was gunned down may have been unintended, but was hard to dispel. Her demand at the weekend that her party award her the maximum number of delegates from the Michigan and Florida primaries even though both were effectively cancelled for timetabling reasons - and even though Mr Obama's name was not even on Michigan's ballots - was scarcely more rational.

Tomorrow, a senior Democrat whip on Capitol Hill is expected to endorse Mr Obama. A flood of super-delegates should follow (see page 32). Mrs Clinton knows what is coming. So where will she go? She could lobby to share the Obama ticket, but would not be best used there. She could bake cookies, but she won't. Her destiny, instead, is to lead the Democratic majority in the Senate. As Lyndon Johnson proved, the Senate majority leader can make or break a president's legislative programme. In his post, Mrs Clinton would be the most powerful woman in US history - and, as either a President Obama or a President McCain could sooner or later find, the most powerful politician in Washington.