With Hillary Rodham Clinton hoping to tack another four or eight "Clinton" years on to the Bush-Clinton-Bush presidential pattern that already has held sway for two decades, talk of Bush-Clinton fatigue is increasingly cropping up in the national political debate.

The dominance of the two families in U.S. presidential politics is unprecedented. (The closest comparisons are the father-son presidencies of John Adams and John Quincy Adams, whose single terms were separated by 24 years, and the presidencies of fifth cousins Theodore Roosevelt and Franklin Roosevelt, whose collective 20 years as president were separated by a quarter-century.)

"We now have a younger generation and middle-age generation who are going to think about national politics through the Bush-Clinton prism," said Princeton University political historian Julian Zelizer, 37, whose first chance to vote for president was 1988, the year the first President Bush was elected. And as for the question of fatigue, Zelizer added: "It's not just that we've heard their names a lot, but we've had a lot of problems with their names."

And now, if Hillary Clinton were to be elected and re-elected, the nation could go 28 years in a row with the same two families governing the country. Add the elder Bush's terms as vice president, and that would be 36 years straight with a Bush or Clinton in the White House.

Already, for 116 million Americans, there has never been a time when there wasn't a Bush or Clinton in the White House, either as president or vice president.

Does a nation of 303 million people really have only two families qualified to run the show?

David Gergen, director of Harvard University's Center for Public Leadership and an adviser to presidents Nixon, Ford, Reagan and Clinton, said there does seem to be concern about the possibility of giving "the two dynasties" another four or eight years.

"I think we would be fundamentally healthier if we broadened the zone of candidates who could make it to the top," he said.

Historically, politics has been open to newcomers who rise up to reflect the grass-roots sentiment of the country, Gergen said.

That's still possible, he said, "but it's harder than it used to be, especially because it's so hard to raise money" for expensive national campaigns.

The Clintons and Bushes, he said, have built up strong "brand" recognition for their names - just as the Kennedys did in an age of promise cut short by assassination - making it harder for newcomers to compete.

But sometimes, people just want to try something new.

An NBC/Wall Street Journal poll taken over the summer found that fully one-quarter of all Americans said that the prospect of having at least 24 straight years of a President Clinton or Bush would be a consideration in their vote for president in 2008.

Even among Democrats, 17 percent said it would be a consideration. That compared with a third of all Republicans.