Reflecting on the obstacles facing any candidate for the White House, the First Lady said, "I think that what the American people don't know is how difficult it is to run for president, to run for office, and how much both emotional and physical stamina you need to run for office and I think that's what George is talking about."
When asked by Gibson whether the candidates could ever know the psychological and physical burdens they might face in office, the President replied, "No, you can't… till you actually get in there, and understand the responsibilities that come with the office, you can't possibly, can't possibly comprehend it."
"I'll tell you one thing that'll surprise 'em if they've got an open heart, is that the prayers of the people will affect 'em in a positive way. That has been one of the most surprising aspects of the presidency for me."
Mrs. Bush admitted she could see the presidency "wearing" on her husband but she said, "He's doing great but, I mean, the seven years have flown by, they really have."
Bush family members and members of the president's inner circle have scattered their support among several Republican candidates, including former mayor Rudolph Giuliani, R-N.Y., former governor Mitt Romney, R-Mass., Sen. John McCain, R-Ariz., and former senator Fred Thompson, R-Tenn.
The president joked that his mother, former first lady Barbara Bush, engineered the spreading around of the family's loyalties.
"My mother wisely has said, 'Okay, you pick this camp, you pick that camp, you pick this camp,' " he said.
Mrs. Bush jumped in to say that the family will line up behind the GOP nominee.
"I'll tell you this, they will be united behind the Republican whoever it is when the nomination [battle] is finished," she said.
See more of the president and first lady on "World News With Charles Gibson" and "Nightline" this evening, and on Wednesday on "Good Morning America."