Why Obama's lead in the polls at this stage means nothing:

Dukakis Lead Widens, According to New Poll

Published: July 26, 1988

...Fifty-five percent of the 948 registered voters interviewed in the poll said they preferred to see Mr. Dukakis win the 1988 Presidential election, while 38 percent said they preferred to see Mr. Bush win. The poll had a margin of sampling error of plus or minus four percentage points.