With his “Potomac Primary” sweep of Maryland, Virginia and the District of Columbia, Barack Obama continued one of the longer winning streaks ever sustained by a candidate locked in a still serious contest for a party presidential nomination. Following a Super Tuesday that saw Obama win most of the day’s twenty-two contests and a roughly even share of the delegates, he has been on a roll, securing victories in states as diverse as Louisiana, Maine, Nebraska and Washington. Add anticipated February 19 wins in Wisconsin and Hawaii, and the Illinois senator’s post-Super Tuesday record could be 10-0.

Those numbers are making February the longest month for New York Senator Hillary Clinton, who loaned her campaign $5 million to get through Super Tuesday and has since then spent too much time holding the hands of big donors and wavering superdelegates rather than shaking the hands of voters. Her campaign, which so enjoyed the expectations game that in 2007 made her the “inevitable” contender, is now suffering the miserable fate of the candidate who keeps losing states that were supposed to be jewels in the nominee’s crown.

With Clinton now trailing in the race for delegates, it has finally dawned on her campaign that if she does not start to win soon, they will face the toughest of all political questions: When does a contender who keeps losing face reality? And if the candidate fails to do so, when will party leaders nudge her aside?

Despite the hopes of Clinton’s backers and the fears of foes that she can rely on the elected officials and party insiders who serve as super delegates to tip a tight convention her way–or that the rules committee will seat pro-Clinton delegations selected in unsanctioned Michigan and Florida primaries–the reality is that what seem like structural safety-nets for a failing Clinton campaign are beginning to look more like intervention points for party insiders whose inclination to go with a winner has traditionally trumped personal and political loyalty. Clinton’s got a super-delegate advantage, but Obama’s right when he says that, “if this contest comes down to super-delegates, we are going to be able to say we have more pledged delegates, which means the Democratic voters have spoken. Those super-delegates, those party insiders would have to think long and hard how they would approach the nomination.”

It’s already happening; DNC Rules and Bylaws Committee member and “star” superdelegate Donna Brazile says, “If 795 of my colleagues decide this election, I will quit the Democratic Party…. There’s no reason why we should decide this election.” While Brazile may just be talking about quitting her leadership position in the party–as opposed to the whole thing–her concern about the role of the super delegates is hardly unique, even among the party elites. A senior House Democrat, also a superdelegate, is blunter: “Anyone who thinks super-delegates are going to impose a Clinton nomination on a party that has rejected her is nuts. No one goes to the mat for a candidate who looks like a loser.”

Clinton is starting to look if not quite like a loser then surely like a candidate in a corner.

Her troubles are rooted in a failure to respond to the Obama challenge as past candidates in Clinton’s position have to similar threats. In 1984, when Colorado Senator Gary Hart’s primary and caucus victories challenged former Vice President Walter Mondale’s inevitability, Mondale countered with his “where’s the beef?” test of Hart’s credibility as an agent of change. In 1992, when Jerry Brown’s $100 donor campaign started winning primaries and caucuses, shaken frontrunner Bill Clinton countered by attacking Brown’s support for a flat-tax as a regressive stance that had to be rejected. In both contests, old-school candidates beat insurgents by delivering a message that rallied the party faithful.

Clinton has yet to develop such an “ask.” Her campaign, which enjoyed an unwarranted reprieve after a narrow New Hampshire primary win, has been slow to recognize the urgency of making a case for why Democrats should choose Clinton over Obama. Now, a shuffled leadership team understands that Clinton must offer the voters of Ohio and Texas–where she has made March 4 primaries her “must-win” races–something more than “experience,” which was losing badly to “change” in February exit polls.

Speaking of the March 4 test, Clinton backer James Carville described his candidate’s circumstance bluntly: If Clinton loses Ohio, he said, “this thing is done.”

While she can count some on the demographics of heavily Hispanic Texas, she won’t win Ohio without a message that echoes the economic populism of former candidate John Edwards and somehow erases memories of her past support for free-trade deals that Ohioans blame for their state’s recent hard times. That’ll be a tough sell, as Obama counters with a fair-trade messaging and a television advertising budget that will overwhelm Clinton’s.

Clinton won’t be able to make any excuses on March 4. After the losses of February, she must start March with wins that restore her delegate lead.

Arizona Senator John McCain’s big wins in the GOP’s “Potomac Primaries” put new pressure on his last challenger, evangelical champion Mike Huckabee, to suspend his campaign. If Huckabee folds–or simply fades away–Democrats, including those super-delegates, will get nervous about talk of their party’s contest “going to the convention.” Unless Clinton is winning then, the only inevitable thing about her campaign will be the calls for her to quit for the sake of both party unity and political realism.