WASHINGTON, Jan. 20. 2005 , 2005 -- President Bush's second inauguration was a day of personal and historical significance for the Bush family, who are now firmly enshrined in the pantheon of powerful political families, historians say.
"Whether one likes it or not, one has to concede that the Bushes are the most successful political dynasty in American political history," said Bush family biographer Peter Schweizer.
The Bushes have been more successful than John Adams and his son John Quincy Adams -- both one-term presidents -- and more successful than the Kennedys, who spent about 1,000 days in the White House.
By the time the current Bush leaves office, someone named Bush will have occupied the White House for 12 of the last 20 years.
Schweizer says the Bushes pride themselves on being the "un-Kennedys" -- more Crawford, Texas, than Camelot.
"They do measure themselves against the Kennedys," said Schweizer, who co-authored "The Bushes: Portrait of a Dynasty" with his wife, Rochelle Schweizer. "They do want to achieve greater political success than the Kennedys and I think that they confidently believe that they have done so."
Mary Matalin, a political adviser who has worked for the Bushes, doubts the claim.
"The Bushes do not sit around and count themselves or their own achievements," she said. "They were taught -- and it's in their DNA -- not to brag."
The Roosevelts -- Teddy and his cousin Franklin -- spent nearly 19 years in the Oval Office, more time than the Bushes, but their power lasted only one generation.
Bushes Adapt to Times
By contrast, the Bush dynasty started with Prescott Bush, a senator from Connecticut, whose son and grandson have both been elected president.
The Bushes have succeeded, in part, by adapting to the times. Prescott Bush, the patriarch, was a moderate New England Republican. His grandson, the current president, is a southern social conservative.
Some wonder if the Bush dynasty can continue in a nation founded in opposition to royalty.
The president's brother Jeb -- current governor of Florida -- has said he will not seek the presidency in 2008, though some are doubtful. Jeb's 28-year-old son, George P. Bush, is also said to have political aspirations.
The future of the Bush dynasty may well rest on the success or failure of George W. Bush's second term and whether he leaves the Bush brand burnished or battered.
ABC News' Dan Harris filed this report for "World News Tonight."