Any future US president will likely be more cautious about launching a preemptive strike against another country following a failure to find evidence of weapons of mass destruction in Iraq, US Secretary of Defense Robert Gates said Wednesday night. Gates told PBS that stricter criteria would have to be used before any future strike. "The lessons learned with the failure to find the weapons of mass destruction, and some of the other things that happened, will make any future president very, very cautious about launching that kind of conflict or relying on intelligence," Gates said. He said that after former US president George W. Bush, any future president would "ask a lot of very hard questions, and I think that hurdle is much higher today than it was six or seven years ago". He added, "I think that the barrier, first of all, will be, 'Are we going to be attacked here at home?'" Gates also said the "quality of the intelligence" was a factor that had to be considered before a preemptive strike. The US's failure to anticipate that the invasion of Iraq would evolve into a drawn-out counterinsurgency operation "was one of the biggest mistakes that was made," he said. Gates's statements came only a week after he asserted that Iran was not close to attaining a nuclear weapon. "They're not close to a stockpile, they're not close to a weapon at this point, and so there is some time," Gates told NBC's Meet the Press when asked whether the Islamic republic could be deterred from pursuing nuclear weapons. The US would continue to pursue additional sanctions, while also leaving an opportunity for Iran to engage with Europe as a means to "walk away from that program," Gates said. However, Adm. Mike Mullen, chairman of the US Joint Chiefs of Staff, said Teheran probably had the material necessary to make a nuclear weapon. Asked on CNN if Teheran had enough nuclear material for the construction of an atomic bomb, Mullen said, "We think they do, quite frankly." "Iran having a nuclear weapon, I believe, for a long time, is a very, very bad outcome for the region and for the world," he said. Herb Keinon and news agencies contributed to this report.