What is Clinton's path to the nomination?
3. Clinton needs at least four things to happen. First, she must significantly narrow Obama's lead in the pledged delegate count. Under almost no scenario is there a way for her to overtake Obama in that column, given the rules of proportionality. But by winning the overwhelming share of the last 10 contests, she can begin to cut down the margin and also claim momentum at the end of the race.
Second, she must also finish the primaries ahead of or nearly tied with Obama in the popular vote. Because she cannot take a lead in pledged delegates and because Obama will have won more states by the end of the primaries and caucuses, she will need the popular-vote edge to give uncommitted superdelegates a rationale to deny Obama the nomination.
At this point she is more than 700,000 votes behind -- more than 400,000 if the Florida results (but not those from Michigan) are included. She will need big victories in Pennsylvania, Puerto Rico, Kentucky and West Virginia to come close. But without new voting in Michigan and Florida, her chances of winning the popular vote are greatly diminished.
Third, Clinton must emerge in national polls as a stronger candidate against John McCain. Clinton has gained ground in recent polls, but the superdelegates will look at the polls in June, not March, before making their decisions.
Finally, Clinton must persuade uncommitted superdelegates to deny the nomination to the candidate who has more pledged delegates. But to side with her would almost certainly offend African Americans, the party's most loyal constituency. How many superdelegates will be prepared for that?
What's not clear is whether Clinton can accomplish all this without a much more negative campaign -- and that could prompt rebukes from party leaders and calls for Democrats to coalesce around Obama.
Has Obama successfully dealt with the controversy over the Rev. Jeremiah A. Wright Jr.?