In a speech to Israel's Knesset, Bush spoke of the president of Iran and warned against appeasing terrorists, which some interpreted as a slap at Obama, who has said he would be willing to meet with heads of state in places like Iran. Obama used Bush's remark to lump the president and McCain together.

McCain aides insist they had no advance knowledge of the president's remarks, and the White House publicly denied the comments were directed at Obama. Still, the episode underscored the pitfalls and benefits — as well as the evolution — of the Bush-McCain association.

In 2000, the two squared off in a bruising battle for the GOP nomination. Bush won but the scars for McCain lingered for a while, and, to this day, GOP operatives can be divided into Bush and McCain loyalists. In 2004, McCain embraced Bush, figuratively and literally, and campaigned on his behalf even as he railed against the president's Iraq policy and called for more troops.

Some two years later, as McCain launched his own White House bid, he found himself on the same page with Bush on Iraq as the president adopted his push for a troop build up. The two also were in agreement on the hot-button issue of eventual citizenship for millions of illegal immigrants in the country.

The combination led some of McCain's core supporters to worry that he was carrying Bush's water, and endangering his own presidential prospects in return.