Washington: Republican Jeb Bush's flirtation with a possible run for the White House in 2016 has been so low key that some in his party aren't convinced he's prepared to take on the challenge.

The former Florida governor with the famous family name is among the leaders in polls charting potential Republican contenders in 2016 and says he will decide late this year or early next year.

But unlike some would-be competitors like New Jersey governor Chris Christie, who are making forward-leaning statements, Bush is publicly expressing his uncertainty.

Questions are weighing heavily on Bush, 61, about the impact on his wife and family and whether he can offer an agenda that would unite Americans.

Whether he will run is a question that comes up almost daily for Bush as he travels the country campaigning for Republican candidates ahead of November 4 congressional elections. On Thursday, he was in Greenville, South Carolina, campaigning with governor Nikki Haley, who is seeking re-election.

"It's a big decision," he told reporters in Greenville. "It relates to family."

"I think the next presidential race has to be about the future and it has to be about fixing some big problems," he said.

"I think it's more than likely that he's giving this a serious thought and moving forward," Bush's son, George P Bush, said on ABC's "This Week" program on Sunday. "The family will be behind him 100 percent if he decides to do it."

Bush's decision-making seems far less advanced than the past Bush presidents were at similar points in their own career, leading some Republicans to raise questions. His father, former President George H W Bush, began preparing for a 1988 run in 1985. His brother, former President George W Bush, was actively planning his 2000 run at this point in 1998.

"There's a scent of activity that goes on in preparation for a serious candidacy that involves a lot of contacts with donors and strategists," said Florida Republican strategist Rick Wilson. "People aren't seeing that from Jeb. I will say he's been more active, been talking to folks, but not to a degree that Chris Christie has been doing."

Friends say Jeb Bush's cautiousness is due to his deliberate manner and his experience watching his father and brother go through what can be a meat-grinding process. They also say he is not expecting to be drafted, recruited or convinced to run. That is not his style.

"This is not a guy who spends sleepless nights staring at the ceiling wondering if he should or should not run for president," said Ana Navarro, a Republican strategist and a friend of Bush.

"He's a disciplined guy and will make this decision like he does most other big decisions, through a serious deliberative process weighing the pros and cons and looking deep into himself. This is a decision that will be made by Jeb, his wife and kids," she said.

If he runs, Bush would be injecting himself into the presidential race in a Republican Party that has moved to the right since he left the governor's office in 2006.

Bush, whose wife of 40 years, Columba, was born in Mexico, has a more welcoming view on immigration than many party conservatives, who criticize his support for comprehensive reform that would allow a path to legal status for undocumented immigrants.

If Bush were to win the Republican primary and become the party's presidential nominee, he would have to convince a majority of Americans that it would be worthwhile to have a third president named Bush in the Oval Office.

Should he run, donors say Bush could get up to speed quickly by tapping a ready network of financial supporters built from his own alliances and from those who supported previous Bush presidential bids.

His father and brother have publicly urged him to run. People who know them say they are unsure of Jeb Bush's plans.

"Jeb is keeping very close counsel on what his future plans are," said Jim McGrath, spokesman for the elder Bush. "I don't think he's ready to make a decision. I think he's being very sincere when he says he will wait until after the election to decide."