Let him declare whatever he wants. All that counts as facts/numbers/math/the winning margin in the end is Who Actually Produces the Legal Magic Number at the roll call of the states here in Denver in late August. (My goodness, I can't even remember 4 months ago...I wonder what the facts on the ground will actually be 4 months hence.)
So basically you want to leave a mere 2 months for the actual campaign against the Republicans. Just September and October.
While throughout Summer, the Republicans alongside Hillary will both be attacking the man you KNOW will be our nominee. You KNOW it'll be Obama.
Of course at this point making Obama lose has become Clinton's goal, just so she has a chance at 2012.