By NANCY BENAC - Associated Press Writer

The first meeting of incoming and outgoing presidents has been arite of passage fraught with emotion, surprises and the rare exchangeof secrets between leaders of opposite political parties.

OnMonday, President Bush will welcome President-elect Obama to the WhiteHouse, and the 43rd and 44th presidents will make nice. This, after ahard-fought campaign in which one of Obama's most effective strategieswas to rail against the "failed policies" of the current president.

It'soften an emotional moment for both the incoming and outgoingpresidents. Although the formal transfer of power is still more thantwo months away, the "psychological transfer occurs then," former vicepresident Walter Mondale once said.

As significant as the first meeting can be, it isn't even mentionedin the Constitution or federal law, so there are no rules governing howto do it.

Putting Campaign '08 in the rearview mirror, "Bush willturn on his boyish charm, and I think he's enough of a political pronot to take the campaign criticism seriously," said presidentialhistorian Leo Ribuffo of George Washington University.

As forpast meetings between once and future presidents, Ribuffo said,"they've been bad, and they've been good and they've been in themiddle."

One of the most analogous transfers of power to theBush-Obama transition occurred when 70-year-old Dwight Eisenhower, aRepublican, made way after two terms for 43-year-old John F. Kennedy, aDemocrat whom the president had derided as a "young whippersnapper" and"this young genius."

After the three-hour meeting, an aide laterdescribed Eisenhower as "overwhelmed by Sen. Kennedy, his understandingof the world problems, the depth of his questions, his grasp of theissues and the keenness of his mind."

It wasn't all about weighty matters of policy, though.

Eisenhoweralso took time to show Kennedy how to use the panic button that wouldbring a helicopter to the back lawn. Eisenhower demonstrated its use,and "Kennedy watched the fluttering helicopter coming down outside thewindows within a few minutes," Kennedy aide Kenneth P. O'Donnell laterwrote.

When Republican Richard Nixon arrived to meet with departingDemocratic President Johnson, the two plunged into deep conversationabout the Vietnam War and the social unrest gripping the country.

"Onthat day our political and personal differences melted away," Nixonwrote in his memoir. "As we stood together in the Oval Office, hewelcomed me into a club of very exclusive membership, and he made apromise to adhere to the cardinal rule of that membership: stand behindthose who succeed you."

As they walked to one in a series ofWhite House meetings, Johnson pulled Nixon into his bedroom, and toldhim, "I wanted you to know about this." He showed Nixon a small safehidden in the wall.

Bush, for his part, setthe stage for an amiable meeting with Democrat Obama when he praisedhis election as "a triumph of the American story, a testament to hardwork, optimism and faith in the enduring promise of our nation." Bushhas promised to help make "America's first wartime presidentialtransition in four decades" as seamless as possible.

"I can'tremember as generous a statement about a winner of the opposite partythan that of Bush on the historic significance of Obama's win," saidFred Greenstein, a professor of politics at Princeton University.

Bush,the son of a president, was no stranger to the White House when he metwith President Clinton in the Oval office for two hours as thepresident-elect in 2000. At the outset, Bush seemed tense, sittingstraight in a wing-backed armchair, his hands clasped in his lap as herubbed his thumbs and tapped his foot. Twice he thanked the presidentfor his hospitality and said, "He didn't need to do this."

Not all meetings between once and future presidents have been a success _ or even come to pass.

PresidentCarter carefully prepared for his meeting with Ronald Reagan, accordingto Mondale, but "it all went over Reagan's head and Carter really wasshaken by it."

Franklin Roosevelt "did not respond to overturesfrom the discredited Hoover," according to Greenstein. "He wanted tomake a fresh start." As a result, Greenstein said, "Hoover was verychilly to him on the ride to the inauguration."

President Truman,who had the presidency thrust upon him without any transition periodafter Roosevelt's death, was eager to provide a smooth transition forhis successor, Eisenhower. Truman arranged for troops to line bothsides of Pennsylvania Avenue for Eisenhower's arrival.