Even before his latest victories, Mr. Obama, of Illinois, had whittled away at the advantages amassed last year by Mrs. Clinton.

He now enjoys a big financial advantage. Her big lead in national polls is gone. By most counts, Mr. Obama can now claim more delegates pledged to him. He has won far more states than Mrs. Clinton, although she won some of the big prizes, like California and New Jersey.

For weeks, Mrs. Clinton and Mr. Obama had approached this race the same way: as state-by-state trench warfare, in the belief that the nomination would go to whoever got the most delegates.

But the latest results suggest that the race might be tilting back to a more normal form, where the goal is achieving a series of splashing victories and thus momentum. That has provided Mr. Obama with the opportunity, which he plans to seize in a more full-throated way starting on Wednesday, to argue that voters across a wide cross-section of the country have embraced his candidacy, and that the time has come for the group that could hold the balance of power, those 796 unpledged superdelegates  party leaders and elected officials who have an automatic seat at the national convention  to follow suit.

“We are in a momentum phase of the process now,” said Tad Devine, a Democratic consultant.

Mrs. Clinton’s advisers dispute that, noting that his victories have come in relatively small states and that she has invested most of her attention in two big contests coming up on March 4: Ohio and Texas. Her aides have long argued that by the end of the voting, the difference between the two candidates in delegate count would be minimal, leaving the final decision to superdelegates, who in their view would favor Mrs. Clinton.

But if party leaders begin to think this is no longer simply a mathematical race to the 2,025-delegate line, that could have big consequences for Mrs. Clinton.

For one thing, if this is an election where a candidate wins by virtue of being seen as winning  a definition of momentum  that would mean that voters in coming states would be influenced by the outcome of earlier races. And Mr. Obama might then be in a position to encroach on Mrs. Clinton’s firewall of Texas and Ohio.