Depends on just how heinous the attack was.
In the immediate aftermath of 9/11, there were in fact voices that said that Bush had created the attacks himself because the press was about to finish its own Florida recount and show that Gore was the legitimate president. Those voices were restricted to the Internet. No one in the Mainstream Media or Congress took the chance of uttering those words.
Don't count on Kerry or anyone else who understands political expedience taking the enemy's side after a future attack.
I was in NYC on 9/11 and in the months afterward, and the patriotic response was universal. Even the muggers stopped working for a while to join the solidarity. A black woman on the subway, who normally wouldn't deign to speak to a man, let along a white man, told me all about her four sons in the service. People who normally would avoid eye contact were talking to each other.
That lasted for several weeks. Then things started to bog down, while congress refused to pass any security measures unless airport security personnel were all given government appointments, joined the public service union, and agreed to vote Democrat. After a month or so it was back to politics as usual. I suspect if Bush had not been so polite he could have rammed a lot more through then. But not later.
That's why you need to seize the psychological high ground immediately.
Democrats in America are evenly divided on the question of whether George W. Bush knew about the 9/11 terrorist attacks in advance. Thirty-five percent (35%) of Democrats believe he did know, 39% say he did not know, and 26% are not sure.
Could an enormous propaganda campaign possibly convince these kooks? I seriously doubt it. They would probably have to be sent to internment camps with the Muslims.