In President Barack Obama's two presidential campaigns, his predecessor loomed large; Obama and Democrats regularly laid the blame for the downtrodden economy at George W. Bush's feet.
When pressed on their pledge to turn the faltering economy around, Obama and Democrats often pointed out that they had inherited the product of the Bush administration's policies.
Bush, however, in his limited public appearances has stayed mute about his successor, maintaining a custom among former presidents that dates back decades. While not all presidents have adhered to the practice, it has created a mostly amicable brotherhood of former presidents.
"George W. Bush is a traditionalist," CNN Senior Political Analyst David Gergen said. "I think he holds to an old-fashioned standard that the presidency is one of the world's greatest fraternities and its members don't criticize each other."
After leaving the White House, Bush made it clear that he was finished with the public stage. Although he has been more public since his presidential library opened in April, Bush has maintained that he will not criticize Obama.
"I don't think it does any good," Bush said Monday in an exclusive interview with CNN's Robyn Curnow in Zambia, where he was helping to renovate a women's clinic. "It's a hard job. He's got plenty on his agenda. It's difficult. A former president doesn't need to make it any harder. Other presidents have taken different decisions; that's mine."
In "The Presidents Club," a book by Nancy Gibbs and Michael Duffy about the fraternity, a Bush adviser says the most the former president will say about Obama's decisions is, "Well, I might have done it differently."
In public, though, Bush has refused to comment on Obama.
"He deserves my silence," Bush said in a March 2009 speech. "There's plenty of critics in the arena. I think it's time for the ex-president to tap dance off the stage and let the current president have a go at solving the world's problems."
Gergen said he feels Bush's silence about Obama stems from how Bush was treated in his last few years in office.
"There was a sense among the Bush people that a lot of this criticism was gratuitous and ill-informed and painful," Gergen said. That could be "part of his staying away from issues with Obama."
When you are president, there are literally only a handful of people in the world who can relate to the pressure, the commitment, the arduous decision making. This unique understanding has led many presidents to rely on one another after leaving office.
Some of these relationships have led to unexpected political friendships.
Despite the fact they faced off in the 1992 presidential election, the relationship of Bill Clinton and George H.W. Bush has been described as father-and-son-like. They are so close that Clinton joked at the opening of George W. Bush's library that he "had become the black sheep son" of the Bush family.
He even jokingly referred to former first lady Barbara Bush as his "mother."
Other presidential relationships have been similarly close. Presidents Jimmy Carter and Gerald Ford, opponents in the 1976 election, grew close in their retirement and worked together on a number of international issues.
President Harry Truman also befriended a predecessor, Herbert Hoover. After working together to restructure the executive branch, Truman called Hoover "the best man that I know of" and an appreciative Hoover wrote Truman to say, "For all of this and your friendship, I am deeply grateful."
Gergen, who served in the White House in four administrations, said that once in the Oval Office you appreciate the "continuity of the office."
"You form part of a chain and each link is important. You almost have a sacred responsibility to keep the office strong," he said.
Breaking the club's rules
Not all former presidents have held their tongue.
Democratic President Jimmy Carter, who served one term in office, has a history of biting criticism of those who followed him in the White House.
In 2007, Carter delivered a blistering critique of the Bush administration, telling the Arkansas Democrat-Gazette "as far as the adverse impact on the nation around the world, this administration has been the worst in history."
Carter hasn't directed his criticism only at Republicans, though. In a February 2013 speech, he faulted the Obama administration for its dealings with North Korea and Iran.