Just because something's true, that doesn't mean you should shout it out:
A top aide to Sen. John McCain said a terrorist attack in the United States would benefit the Republican nominee politically, a comment that was quickly denounced by the candidate while campaigning in California.
The fact is that many Americans, rightly or wrongly, distrust Democrats on national security, so a terrorist attack probably would help McCain. Likewise, major a economic upheaval would help Obama; indeed, anxiety about the economy is already redounding to Obama's benefit.
Saying something is so is not the same thing as hoping it will happen. But it can seem so, and one's opponents are sure to try to strengthen that impression, which is why this was such a stupid thing to say. And it wasn't off the cuff -- it was in a magazine interview, which most people understand requires reflective answers.