Bush, though, maintained during an appearance in northwestern Pennsylvania that he would not criticize President Barack Obama, though he did discuss his policies.
"I will just tell you that there are people at Gitmo who will kill Americans at the drop of a hat," the nation's 43rd president said at a dinner held by a group of business leaders in Erie. "Persuasion isn't going to work. Therapy isn't going to change their mind."
Bush has made just a handful of public appearances since he left office in January, though his hour-long session before a friendly crowd of about 1,600 touched on familiar themes in reminiscing about his eight years in the White House.
The topic of Guantanamo Bay arose during a question-and-answer session, in which e-mailed or submitted questions were screened and chosen by a moderator during the event.
"I certainly hope not," Bush answered when asked if he thought Obama's plan could compromise security before adding, "I told you I would not criticize my successor."
Bush reminded the audience that he had also remarked during his presidency that he thought the detention facility should eventually close, and that detainees should be able to have hearings — referring to military tribunals.
"I just want to make sure that when people have a hearing ... we don't have to give away our secrets in order to protect you," he said, drawing applause.
On Iran, Bush said he was troubled by its leaders' use of the Revolutionary Guard, the country's powerful military force, and that he was concerned about cries that the recent national election was a sham.
Bush demurred when asked who could lead his own Republican Party in the 2012 presidential race, saying he would wait until at least after the 2010 midterm elections.
"Invite me back — I'll give you my opinion," he said.
Talk about the economy and the recession took up much of the evening. He said U.S. businesses — and not the government — will be the engine to a financial resurgence.
The free enterprise system "will work again, which gives me great confidence if government just releases the ingenuity of the American people, if we provide incentives for people to take risk ... we'll come out of this thing better than before," Bush said.
He was roundly applauded after giving an immediate answer to a question about how to make the manufacturing sector more vibrant. "Low regulations, no frivolous lawsuits and export markets," he said, before also adding support for research and development tax credits.
Among those in attendance in Erie were former first lady Laura Bush and Penn State football coach Joe Paterno, a Republican and supporter of Bush's father, former President George H.W. Bush.
A Bush spokesman declined to comment when asked how much Bush was paid for the appearance.