Des Moines, Iowa ? Seeking the presidency is harder the second time around.

As the race for 2008 builds, Democratic Sen. John Kerry has left little doubt about his intentions to try again after his narrow loss to President Bush in 2004. He isn’t the only also-ran considering another marathon.

Sen. John McCain, R-Ariz., has the look of a White House hopeful. Three Democrats – 2004 vice presidential nominee John Edwards, retired Army Gen. Wesley Clark and Sen. Joe Biden of Delaware – sound a lot like presidential candidates; Al Gore, the Democrats’ nominee in 2000, says he has all but ruled out running for president in 2008.

Kerry faces a challenge of major proportions, convincing Democratic activists that a candidate who just lost an election can still carry his party’s White House hopes.

“I think the Democratic Party, unlike the Republican Party, has had a historic reluctance to give people a second chance,” said Democratic activist Jerry Crawford, a Des Moines lawyer who was chairman of Kerry’s 2004 campaign in Iowa.

It’s rare when Democrats give the nomination to a candidate who just failed.

Adlai Stevenson got a second chance against President Eisenhower in 1956, but many suspect that Democrats were pessimistic about the odds of unseating a popular president. Their doubts were realized when Stevenson lost again.

Republicans, on the other hand, are more willing to give their nominees another try. Richard M. Nixon lost the presidency in 1960 and won the White House in 1968.