Presidents George W. Bush (search) and Bill Clinton (search) are unlikely partners, given their political differences. But their membership in the oh-so-exclusive club of American presidents has forged an increasingly warm bond and melted away some of the old bitterness.

When he needed someone to head up a tsunami-relief effort, it was natural for Bush to reach out to his father, the first President Bush.

Inviting Clinton on board came despite years of political rancor by the Bush family toward the Arkansas Democrat. After all, Clinton had ousted the elder Bush from office in 1992 and campaigned for Democratic nominee John Kerry just last year.

The two former presidents and old rivals now are appearing together in a public service television advertisement to raise funds for the tsunami victims. Earlier, they did several joint TV interviews.

The pairing showed that the two parties can come together for noble as well as ceremonial purposes, following two other recent harmonious gatherings of ex-presidents: Ronald Reagan's funeral in June and Clinton's library dedication in November.

If Clinton and the elder Bush prove successful on their fund-raising mission, as they seem to be doing, Bush might want to consider other projects for them.

"It might be a way for Bush finally to get around to paying off on this notion that he's a uniter, not a divider," Princeton political scientist Fred Greenstein said.

"I think that this business of bonding Clinton with Bush's dad might be a bridge" toward finding bipartisan solutions to some of the nation's thorniest problems, Social Security, for instance, Greenstein said.

But don't hold your breath, say people in both parties.

The GOP's right wing still harbors much hostility toward Clinton. Democrats see Social Security (search) as one of the few bedrock items on which they have a real toehold, especially among older voters. There is broad Democratic opposition to Bush's plan to set up private investment accounts in exchange for cutting guaranteed future benefits.

If not Social Security, then perhaps other issues. Or perhaps Bush will give Clinton a high visibility post. There have been suggestions, even from some Republicans, for Bush to name Clinton president of the World Bank (search) when the job comes open in June.

Bush has been lavish in his recent praise of his predecessor.

"A fellow in Saline County (Ark.) was asked by his son why he liked Governor Clinton so much. He said, 'Son, he'll look you in the eye, he'll shake your hand, he'll hold your baby, he'll pet your dog all at the same time,'" Bush joked at the Clinton library dedication.

Some conservatives are baffled why Bush has been so nice to Clinton. But there are past precedents for such outreach.

President Truman put former President Herbert Hoover in charge of a commission that led to major governmental reforms. Clinton invited former President Nixon to the White House — the first president to do so after Nixon's resignation in the Watergate (search) scandal — and sought his advice on foreign policy issues. Clinton also gave a moving eulogy at Nixon's 1994 funeral.

Ex-presidents are "singularly unique," former President Bush said. "There is an inescapable bond that binds together all who live in the White House."

Well, that may not necessarily include Jimmy Carter (search). More active on public policy issues than any other past president, Carter and his freelance diplomacy in North Korea, Kosovo, Haiti and Cuba have posed problems for Democratic and Republican successors alike.

He was conspicuously missing at last week's White House tsunami relief announcement. Gerald Ford, at 91, was seen as too frail to participate.

Asked why Carter was not invited, White House spokesman Scott McClellan said only that his boss "appreciates these two individuals undertaking this effort. ... It's not why someone wasn't, it's why these people were."

Carter's office in Atlanta issued a statement saying Carter "wholeheartedly supports" the presidential relief efforts and noted that he had a busy schedule that include a trip to the Middle East for Sunday's Palestinian elections.

Carter has criticized Bush over the Iraq war and invited Bush-bashing filmmaker Michael Moore to his box at the Democratic National Convention (search).

As the elder Bush worked to build U.N. support for the first Persian Gulf War, Carter privately lobbied Security Council (search) members against the effort. "President Bush was furious at this interference in the conduct of his foreign policy," wrote Brent Scowcroft, national security adviser for the elder Bush.

Stephen Hess, who served in the Eisenhower and Nixon administrations and advised Carter during his transition to the presidency, said sitting presidents "recognize that former presidents can be useful. In moments of crisis, when we really need rally-around support, you call them in. And they're sympathetic."