After 16 years, the Clinton era may be coming to an end, presenting Democrats with a historic but potentially wrenching transition and a challenge to Senator Barack Obama as he seeks to reconcile a deeply divided party.

And while the relationship between the party establishment and the Clintons has always been uneasy at best, an entire generation of Democrats has known no other figures as dominant as the two of them.

But Mr. Obama’s move to the brink of the nomination was fraught with symbolism and evidence of a party in transition. A first-time presidential candidate, he has so far outmaneuvered the vaunted Clinton political machine. He positioned his candidacy as a repudiation of the kind of politics the Clintons practiced and a generational break. And he drew thousands of new voters and donors into his fold, giving the party a fresh face and new energy.