"The Commission believes that unless the world community acts decisively and with great urgency, it is more likely than not that a weapon of mass destruction will be used in a terrorist attack somewhere in the world by the end of 2013."
In other words, Senator Graham wants the world to know that a panel of experts has predicted we have a better than 50-50 chance of a terrorist attack involving some kind of WMD in the next five years. The panel further predicted, elsewhere in the report, that the weapon to be used is more likely to be a biological agent than either chemicals or nukes. Nowhere in the report did they describe the methodology, if any, they used to make those predictions.
Senator Graham has also made this, even bolder, prediction:
"If we were to ask any person who has a reasonable knowledge of the capabilities of terrorists and the extent of America's vulnerability the question, what is the likelihood the United States of America will suffer another successful terrorist attack on our homeland within the next 5 years, the consensus answer is certainly going to be almost a 100 percent likelihood of a successful attack."
Senator Graham made the above prediction on March 4, 2004 (you can read it here, in the Congressional Record, about 15 paragraphs into page S2014), so we'll have to wait three more months to see if he will be proved right. Of course, he can never be proven wrong, even if there is no attack by next March, since he hedged his bets by making the warning hypothetical and by using the word "almost."
His warning about weapons of mass destruction is even slipperier than his 2004 prediction, since: (1) it's much more modest, claiming only a little better than coin-flip odds, (2) it covers the entire world versus just the United States, and (3) it doesn't specify that the attack will be successful. He goes out on a limb only be saying this future attack will involve some kind of WMD.
Such non-falsifiable alarmism works best when it sunsets after five years. That's soon enough to call for immediate action, but still so far off in the future that the predictor won't lose credibility if his warnings don't pan out. Paul Elhrich's many predictions and quotes on environmental and economic topics pretty much define the art form of mid-term scaremongering. All his past predictions have been wrong, but evidently the public has too short an attention span to hold that against him, since his books keep selling.
I can confidently make three predictions of my own. First, neither Senator Graham nor anyone else will mention his previous warning when March 2009 comes and goes without an attack. Second, no one will remember his latest warning when 2013 arrives. Third, Senator Graham will continue to renew his terrorist attack predictions in five year increments as long as he is in public life.