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The 2016 presidential race could be a matchup of two familiar last names: Hillary Clinton, left, and Jeb Bush.

(The Association Press/file)

WASHINGTON (AP) — Again? Really?

There are more than 300 million people in America, yet the same two families keep popping up when it comes to picking a president.

The possibility of a Bush-Clinton matchup in 2016 is increasingly plausible.

After months of hints and speculation, former Florida Gov. Jeb Bush last week said he's actively exploring a bid for the Republican nomination.

And while Hillary Rodham Clinton hasn't revealed her intentions, she's seen as the odds-on favorite for the Democratic nomination.

Between them, the two potential rivals have three presidents and a U.S. senator in the branches of their family trees. And three governors, as well.

Why are these two families so dominant in modern politics?

It turns out that even though Americans profess to reject dynasties, in politics they're quite comfortable with familiar names.

And a famous name can bring a candidate instant brand recognition, important fund-raising connections and a ready network of political contacts. It may also suggest competence at a time of dysfunction — like now.

"Power begets power," says Dartmouth College political scientist Brendan Nyhan. "Dynasties can self-perpetuate."

A political pedigree can have its negatives, though. A prominent surname sometimes carries unsavory associations and the risk of a fatigue factor.

Both sides of that equation were evident after Bush, 61, the son and brother of a president and the grandson of a senator, made his announcement.

Party activists said the Bush name would help Jeb attract early money, talent and supporters around the country.

But Bush's brother, George W. Bush, was hugely unpopular at the end of his presidency six years ago. And while people seem to think more of him now, the recent release of a Senate report on Bush-era torture practices was a ready reminder of past controversies.

Clinton, 67, a former secretary of state, senator and first lady, will face the same competing dynamics of familiarity vs. fatigue if she enters the race.

Former President Bill Clinton is enormously popular now, and would be sure to campaign for his wife as he did in the 2008 race, but there is still plenty of lingering unwanted baggage from his White House years.

After Bush edged closer to a run last week, the liberal RootsAction group quickly set up a NoBushesorClintons website and began collecting signatures on a "declaration of independence" that pledges to "reject future domination of government by the Bushes and Clintons and by Bush/Clinton-like policies."

But Princeton historian Julian Zelizer thinks the comfort element might be more important to 2016 voters than any same-old, same-old worries.

"Washington's broken, and voters and campaign donors are looking for people who seem to know what they're doing," he said. "The familiarity of these names becomes a big benefit and counteracts any sense that, 'Oh my God, I can't believe these are going to be the candidates again.' "

Despite some groaning about a possible Bush-Clinton sequel, there's plenty of reason to think voters will simply take a breath and size up the primary election candidates on their merits.

"It's all about alternatives," Zelizer says. "If that's the best choice available, people will get over it."

Dynastic politics, in which multiple family members hold elected office, are more common than people might think in the U.S.

The U.S. has had 44 presidents, and eight of them came from four families. (Two each of Adams, Harrison, Roosevelt and Bush.)

Nyhan points to a 2010 study published in Legislative Studies Quarterly that found that over the previous two centuries, nearly 9 percent of members of Congress were closely related to someone who had served in a previous Congress. It concluded that such politicians "enjoy 'brand name advantages,' giving them a significant edge over comparable nondynastic opponents."

That kind of talk makes Jeff Cohen's skin crawl.

Cohen, a co-founder of the RootsAction group, said even his non-political friends frequently complain about the dominance of the Bushes and Clintons.

"It's a source of frustration and it's broad," he says, calling the Bushes and Clintons "symbols of a corrupt system and a permanent governing class."

Even Bush's mother has suggested a third President Bush could be one too many.

"If we can't find more than two or three families to run for high office, that's silly," she said earlier this year.

(Mom supposedly has since come around to the idea of another Bush candidacy.)

Clinton, for her part, may have to worry as much about Obama fatigue as she does about Clinton fatigue.

"She served in Obama's Cabinet, she's been around a long time, and she's quite old for a presidential candidate," says Nyhan. "So the Republicans have an opportunity to run a turning-the-page campaign against her."

Of course, if she's running against a Bush, that's a harder case for Republicans to make.