Senator Barack Obama emerged from Tuesday’s primaries leading Senator Hillary Rodham Clinton by more than 100 delegates, a small but significant advantage that Democrats said would be difficult for Ms Clinton to make up in the remaining contests in the presidential nomination battle.

Neither candidate is expected to win the 2,025 pledged delegates needed to claim the nomination by the time the voting ends in June.

But Mr Obama’s campaign began making a case in earnest on Wednesday that if he maintained his edge in delegates won in primaries and caucuses, he would have the strongest claim to the backing of the 796 elected Democrats and party leaders known as superdelegates who are free to vote as they choose and who now stand to determine the outcome.

Ms Clinton’s aides said she could still pull out a victory with victories in the biggest primaries still to come, including Ohio and Texas next month.  But Mr Obama’s clear lead in delegates allocated by the votes in nominating contests is one of a number of challenges facing her.

With every delegate precious, Mrs Clinton’s advisers also made it clear that they were prepared to take a number of potentially incendiary steps to build up Mrs Clinton’s count. Mrs Clinton won more votes than Mr Obama in both states, though both candidates technically abided by pledges not to campaign actively there.

Mr Obama’s aides reiterated their opposition to allowing Mrs Clinton to claim a proportional share of the delegates from the voting in those states. The prospect of a fight over seating the Florida and Michigan delegations has already exposed deep divisions within the party.

Much for Mrs Clinton depends on shoring up her support in the portions of the electorate — including women, low- and middle-income voters and Hispanics — that have provided her with victories in key states.