An al-Qaeda attack on US soil.
An attack of that type would play into John McCain's hand. And looking at the last 8 years, as far as OBL is concerned WTC was the most successful mission in the history of the world. George Bush fell into his trap, declared unwar on Islam, and the United States has suffered grievously.
There is nothing OBL would like more than a continuation of those policies, and the be able to fight Americans anywhere, to drain the treasury and cost America it's moral values and leadership.
That means OBL woudl love McCain.
Arf