– Remember presidential contenders Rudy Giuliani? Gary Hart? Mitt Romney's father?

They were front-runners in national polls at this point in past presidential election cycles. By the time people actually started voting, they were afterthoughts.

That's why today's top-tier candidates shouldn't get smug. Not even Hillary Clinton.

"People aren't paying much attention right now," said Andrew Kohut, director of the Pew Research Center.

Rarely in the past 50 years has a non-incumbent Democrat led year-before polls and become the party's presidential nominee. The exception was former Vice President Walter Mondale, a Democrat who held on through 1983 and 1984. Mondale, of course, got shellacked in the general election by Republican President Ronald Reagan.

Other than that, starring in an odd-numbered year means about as much as scoring a field goal in the first quarter of a football game. There's too much time left for the opposition to regroup.

It doesn't always work out

Some early front-runners wound up not running, such as New York Gov. Mario Cuomo in 1991. Some were leveled by underdog insurgents, such as 1971 favorite Sen. Edmund Muskie, D-Maine, who fell to Sen. George McGovern, D-S.D.

Others were victims of their own gaffes, notably Michigan Gov. George Romney in 1967, a Republican who said American generals and diplomats gave him a "brainwashing" about the Vietnam War.

Some benefited from being well-known, but only until others caught up. Adlai Stevenson had already run twice in the 1950s and was a 1959 front-runner, but John F. Kennedy wound up the Democratic nominee. Sen. Joe Lieberman of Connecticut was the 2000 Democratic vice presidential candidate and led party polls through much of 2003. He ran a distant fifth in the first-in-the-nation New Hampshire primary and was soon gone from the race.

Eight years ago, Clinton was the strong favorite while barely known Barack Obama was starting his third year in the U.S. Senate.

She led the University of Iowa survey in August 2007, but by December, polls in the nation's first caucus state showed a virtual tie with Obama and former North Carolina Sen. John Edwards. In January, Obama easily won the caucus and Clinton finished third.

Giuliani, the former New York City mayor, was an exception. He had a wide lead in early 2007 polls, then faded fast as Sen. John McCain, the eventual Republican nominee, and former Massachusetts Gov. Mitt Romney surged.

For some candidates, early leads are mixed blessings.

This year's rising star so far is Wisconsin Gov. Scott Walker, who has vaulted into the top tier of possible 2016 Republican presidential candidates. His showing "can be very helpful, because it gets you known fast," said David Woodard, a Clemson, S.C., Republican consultant.

Benefits of early strength

That name recognition could help Walker raise money and woo big-name staffers, Woodard said.

It also means new attention to Walker's record, temperament and behavior, and sometimes that scrutiny can hurt.

Walker seems to relish the notion that he's the man to beat. After Obama criticized Wisconsin's new right to work law, Walker told an audience, "It suggests maybe we're the front-runner if somebody is taking an active interest in what a state governor is doing."

Ask Gary Hart, the 1987 Democratic front-runner. His campaign imploded that May when he was found spending a night with a woman other than his wife. Michael Dukakis became the 1988 nominee.

What about 2016? Clinton is enduring new scrutiny of her e-mails while she was secretary of state. She slipped 6 percentage points in a CNN/ORC poll of Democrats this month.

There's ample time for front-runners to become has-beens and then take the lead again: The Iowa caucuses will be held on Feb. 1, 2016, and New Hampshire's primary election is set for Feb. 8, 2016.