With each passing day, it seems more certain that Barack Obama will do what was once unthinkable. As his deficits in Ohio and Texas polls shrivel to preclude the possibility of catastrophic defeats that would put the race back into play, Obama will almost assuredly defeat the most powerful and gifted Democratic family in existence to win the nomination of the party, which they singlehandedly lent relevance to for some time.

And when the dust settles around a sealed Obama nomination after the March 4 primaries, the hard part will begin.

It will not be a cakewalk to the White House. John McCain is a highly respected candidate, and his name on the ballot will give Americans of diverse backgrounds and ideologies pause come election time, if nothing else. To defeat McCain, the Obama camp faces an entirely new set of challenges.

One of these challenges is for Obama to continue to meet the astronomical expectations he has set for himself as a candidate and human being. As conservative columnist William Kristol noted in The New York Times this week, though Obama’s rhetoric seeks to empower supporters by suggesting he is a symbol of their own desire to work toward a conciliatory political climate, his candidacy’s implied raison d’etre is that he is a singular force of change the likes of which Americans will not see again.

“Obamania” is only made possible by the man’s unique combination of qualities: proven intellect, multinational ethnic heritage, non-contradictory political record, traditional family life, unimpeachable ethics and just enough experience in federal government to demonstrate competency while still allowing him to refer to Washington as “the other.” Take away one of these, and he might cease to be such a source of inspiration.

So, if we were to see less-than-beatific behavior from Obama in the long second leg to the presidency, whether in the form of unearthed political inconsistencies or skeletons from his personal history’s closet, would he continue to dominate? If a certain flaw is revealed that makes Obama seem incapable of being a “uniter,” or even simply less than perfect, will his campaign lose steam? Obama’s approach demands perfection, and it is one that can be both enormously successful and extremely volatile.

It also remains to be seen whether Obama can capitalize on the bipartisan support surrounding his campaign as we enter the more polarized general election stage.

American presidential campaigns are personality-focused, and never more so than in pre-nomination. Character traits are decisive in early votes because party compatriots tend to run on very similar platforms. Democratic debates this season have been a perfect example — on every major issue it seemed as if there was an echo in the room. Candidates are really only composed of two variables — policy and persona — and when distinctions in the former are close to nil, selections are based on the latter.

Thus, it has been Obama’s immense capacity to inspire, not the particulars of his policies, that has been instrumental in carrying him to the brink of first-round victory.

But I’m afraid this curiosity will become extinct in the harsher environs of the general election. Unlike intra-party contests, McCain-Obama will not only offer voters two unique personalities and biographies, it will present two drastically different policy platters.

Contrary to the Clintons’ contention, Obama’s campaign is proposing many bold, substantive changes. Perhaps complicating dreams of bipartisan unity, many of these — including making the social security tax code more progressive, cutting corporate tax loopholes and slowing the pace of trade liberalization — are at odds with economic policies traditionally favored by Republicans.