"For some reason everybody in the establishment is chanting that Santorum and I should quit. Romney has to earn this. It's not going to be given to him," he said. At the same time, his aides were explaining that he had pushed out his campaign manager, trimmed his staff by one-third and would cut back on personal campaign time in primary and caucus states in favor of contacting unpledged delegates.
Another sign that the Gingrich campaign had entered an end stage: Casino mogul Sheldon Adelson, whose family has donated millions to a Gingrich-friendly super PAC, said that "it appears as though he's at the end of his line." The remark, reported Wednesday by JewishJournal.com, came Monday as Adelson informally discussed the race during a leadership retreat in Las Vegas.
The Associated Press tally showed Romney with 568 delegates and on a pace to reach the required 1,144 in the remaining primary and caucus states. Santorum has 273, and Gingrich 135.
Romney has reaped several endorsements in the past week, since trouncing Santorum in the Illinois primary.
Bush has long been in his corner, but aides to Romney said Thursday's event was something different, a formal endorsement from the ex-president and his wife, Barbara.
Bush's son was generally viewed as the more conservative president of the two, but his popularity waned among Republicans as well as Democrats and independents when the economy cratered in 2008.
Associated Press writers Thomas Beaumont in Iowa and Steve Peoples in Washington contributed to this report.