An unspoken question hovering over the Republican presidential race here is why Mr. Bush, the state's popular former governor and heir to the nation's aging political dynasty, has not added his voice to the party establishment's support for Mr. Romney in his increasingly bitter duel with Newt Gingrich.
It has not been for a lack of effort by Mr. Romney, who has made phone calls, traded e-mails and met privately to try to win over Mr. Bush. The campaign was poised to make him a national co-chairman, a role Mr. Bush would have shared with Gov. Chris Christie of New Jersey, but several Republicans familiar with the offer say it was declined. As the center of Republican politics has once again returned to Florida, with Mr. Romney and Mr. Gingrich making final appeals to voters across the state on Sunday, Mr. Bush has been noticeably — and, several friends say, purposefully — absent from the conversation.
"If Dad got behind him, that would help shut the door," Jeb Bush Jr., his youngest son, said in an interview, referring to Mr. Romney. "But that's just not his style."
Mr. Bush has made clear in television interviews and in conversations with friends that he is troubled by the sharpening tenor of the race, particularly on immigration. He voiced his concern directly to Mr. Romney, two people close to him said, urging him to moderate his oratory and views to avoid a collapse of support among Hispanic voters in the general election.
In his conversations about an endorsement, Mr. Bush also conveyed to Mr. Romney and his allies that his double-digit defeat in the South Carolina primary did not warrant an endorsement and he needed to "earn" it. Yet if weekend polls showing Mr. Romney with a double-digit lead offer an accurate picture of the race, an endorsement from Mr. Bush may be unnecessary.
The level of effort and intensity by the Romney campaign to court Mr. Bush suggests that his seal of approval was highly coveted not only for the Florida primary, but also in the quest to galvanize the party behind him to help swiftly lock down the Republican nomination.
"Of course, everyone wants him to endorse," said John D. Rood, a finance chairman for Mr. Romney in Florida, who was also ambassador to the Bahamas under President George W. Bush. "But I think Jeb looks at his endorsement as one where he wants the people of Florida to study the issues, work hard and make an educated decision."
A series of false reports last weekend suggested that Mr. Bush was on the verge of endorsing Mr. Romney. The rumors, which some aides to Mr. Romney were initially promoting, agitated Mr. Bush, who was in China at the time and unable to quickly respond.
For the last year, as Republicans have openly pined for a wider field of presidential candidates, Mr. Bush's name has been atop the wish list. His low-key posture in the race has done little to cool speculation about the aspirations of Mr. Bush, 58, the son of one president and the brother of another.
If he is thinking of ever running for president himself — as many of his friends believe that he is — he also could have concluded that it was not in his interest to get involved and agitate conservatives in his party by going against Mr. Gingrich. He has often chosen not to become embroiled in primary races here in Florida.
But his silence in the fight between Mr. Romney and Mr. Gingrich has been noticed by Republicans here. As the two candidates made appearances on Friday before Mr. Bush's Hispanic Leadership Network, Mr. Bush was not in the audience. He turned up later that day in Washington for a private Oval Office meeting with his father and President Obama.
Former President George Bush has endorsed Mr. Romney. Former President George W. Bush has told friends that he is following the race but has no plans to become involved. All three Bushes were at the Alfalfa Club dinner in Washington on Saturday night, when Mr. Obama joked that many people hoped Jeb Bush would run for president.
"I am not one of them," Mr. Obama declared at the private dinner, one attendee said.
The Republican presidential campaign in Florida, which has erupted into a confrontation between the party's establishment supporting Mr. Romney and conservative grass-roots activists backing Mr. Gingrich, is also infused with a subtext about Mr. Bush. At campaign rallies last week, when asked whom they planned to support, several voters said that they wished Mr. Bush were a candidate.
They are not alone.
When Laura Bush, the former first lady, visited Sarasota this month, she told an audience that Jeb Bush would make a "wonderful" president and that she and her husband wished he had declared his candidacy. "We wanted him to this time," Mrs. Bush said, according to an account in a local newspaper.
For his part, Jeb Bush has played down the likelihood of a presidential run. Some friends have suggested that a vice presidential candidacy would be his best path to the White House, given the resistance that may remain in the electorate after his brother's presidency.
"Never say never," Mr. Bush said in an interview with CNN, responding to a question about a future presidential bid. "But in all honesty, this was probably the right time for me, in terms of my age and just the opportunity that existed, but there are personal and family reasons that made that impossible."
And even as a growing movement of establishment Republican began rallying behind Mr. Romney last week, Mr. Bush declined to tip his hand.
"I've already voted, I voted absentee," he said in the television interview. "And thank God it's a secret ballot."
