In the plus column: Momentum, breadth. In the other: Math

Now that Sen. Hillary Rodham Clinton has shown that persistence pays off, with her comeback victories in the Ohio and Texas primaries on Tuesday, a new question immediately confronts her and her campaign: Can she persevere to ultimately win the nomination?

While she won both those states and Rhode Island, she scored a net gain of only about a dozen convention delegates, leaving her 101 behind Obama. He now has 1,567 delegates to Clinton's 1,462, according to the Associated Press. A total of 2,025 is needed to nominate.

Obama has the lead, but Clinton has the momentum and a strong argument: that she's prevailed in the big, diverse states that the Democratic Party needs to win the White House. That argument could be important if the race ultimately is decided by the 796 superdelegates, who control about 20 percent of the convention's votes.

Superdelegates were created in the early 1980s to balance the sometimes extreme views of party activists. The goal was to help give the party its best chance to nominate a candidate who could win in November.

Talking to the superdelegates

While the current superdelegate count favors Clinton, more than 300 remain undecided. They're all unpledged; any one of them can switch loyalties at any time. Clinton seemed to be talking directly to those delegates Wednesday. "New questions are being raised. New challenges are being put to my opponent," she said. "Superdelegates are supposed to take all that information on board, and they are supposed to be exercising the judgment that people would have exercised if this information and challenges had been available several months ago."

Clinton's also suggesting that if she wins Pennsylvania, the superdelegates should consider the breadth of her vote-getting appeal.

The New York senator has won New York, California, New Jersey, Massachusetts and other large states -- or as supporter Sen. Charles Schumer, D-N.Y., put it Wednesday, "she's won states with 263 electoral votes," seven short of the number needed to win the presidency.

Pennsylvania looks like classic Clinton country. "If I were Hillary Clinton and I had to pick a big state for my final showdown, I'd pick Pennsylvania," said Clay Richards, who conducts Pennsylvania polls for the Quinnipiac Polling Institute.

Clinton blew Obama an air kiss on Wednesday when Harry Smith of CBS told her that "a lot of people in Ohio" said they wouldn't mind a Clinton-Obama ticket. "Well, that may, you know, be where this is headed," she said, laughing. Later, her chief strategist Mark Penn said only that the campaign is focused only on winning. Obama, too, wouldn't discuss any such ticket.

The New York Times contributed to this report.