Here is the best comparison I've seen on the voting coalitions of Hillary Clinton and Barak Obama. It sheds light on the true picture of the electoral landscape, and brings into focus cold facts that the Obama campaign does not publicly admit they see.
For the good of the party, to give the Democrats the best shot to win the White House and turn the country around, Obama needs to put his ambition aside and get real. His delegate lead, grossly inflated as the result of poorly attended caucuses that are historically not a predictor of actual electoral success, is real, but does not translate into meaningful electoral votes come November.
The best candidate to defeat John McCain is Hillary Clinton. She is more qualified, fully vetted, tenacious, intelligent, respected around the world, and has the voting coalition in place right now to do win the presidency.