Forceful, charismatic and controversial, the Clintons are the most sought-after stars in the Democratic Party, reminders of White House glory days and an administration willing to wage fierce fights with Republicans.
On Monday night, the Clintons will give prime-time speeches to rouse Democrats and lure undecided voters for the tough race against President Bush (search).
The only problem is that Kerry may suffer by comparison, making Democrats wistful for a more dynamic candidate, one who doesn't have to struggle so hard to connect with voters.
"Nobody makes the case for the Democratic agenda better than Bill and Hillary Clinton," said Democratic strategist Bruce Reed, who was domestic affairs adviser in the Clinton White House. "They've brought the house down at past conventions and in Boston they'll no doubt do the same."
Where Bill Clinton is eloquent, Kerry is halting. Where Hillary Rodham Clinton is fiery, Kerry is stiff.
Even President Bush recently described former President Clinton as a man of "incredible energy and great personal appeal."
By contrast, The Economist magazine described Kerry as "the political equivalent of Valium."
"Nobody doubts that he's intelligent, but where's the energy and the passion?" said Margaret Thompson, a political scientist and historian at Syracuse University. "He's got to somehow connect" and avoid being "so kind of dry and arid."
The Clintons have a delicate assignment Monday: Be good but don't steal the show. Deliver inspiring speeches but don't be hard-edged. Motivate voters but don't make it too memorable.
After all, it's Kerry's convention.
"They're not going to overshadow Kerry," said Harold Ickes, a leading Democratic fund-raiser and Clinton's former deputy chief of staff. "Kerry is the nominee of the party. He's running for president. People are focused on who's running for president. That is the beginning and the end of it."
Ickes acknowledges that Clinton will have to balance his remarks, rallying Democrats without scaring off people still on the fence.
"There's nobody better to walk that tight wire, as we know, than Bill Clinton," Ickes said. "He'll understand the modulation that he has to hit in terms of his role in this campaign."
The former president is still popular, with an approval rating in the low 60s -- about the same as when he left office.
Hillary Rodham Clinton, serving her first term in the Senate, is a front-runner among Democrats for the next presidential race if Kerry fails this time. Her supporters were outraged when she was omitted from the original lineup of convention speakers. She was quickly added to speak and introduce her husband.
Her speech will be watched closely for hints about her political ambitions.
"People will endlessly turn over Hillary Clinton's remarks for what's there and what's intended and what people think was intended," said Steve Grossman, who served as a Democratic national chairman under President Clinton.
Leading Democrats say the senator will work unstintingly for Kerry's election.
"Would you know it if she didn't? You could tell right away," said former New York Gov. Mario Cuomo.
Some people think Sen. Clinton's speech will help deal with some of her husband's political baggage.
"Her presence undercuts any clear memories of the Monica Lewinsky (search) thing because you're seeing her introduce her husband," said Thompson, the Syracuse professor. "It would be almost indecent to bring up Monica Lewinsky in there."
Moreover, Thompson said, some people regard Sen. Clinton as too strong a woman, and her convention assignment of introducing her husband "is a very traditional kind of role for a woman to play."
Four years ago, Clinton and his wife gave the opening-night speeches at the Democratic convention in Los Angeles and then successfully got out of the way for Al Gore to take center stage. Like Kerry, Gore always paled by comparison with the Clintons but that did not mar his convention.
Significantly, Kerry will speak three nights after the Clintons' remarks, reducing chances of one-to-one comparisons.
In recent months, both Clintons have been in the spotlight as best-selling authors, and some Democrats fretted that the former president's just-published book, "My Life," would cast a shadow over the Kerry campaign with reminders of the Lewinsky affair.
Clinton's book has sold more than 1.5 million copies since its publication June 22 and he has not shied away from promoting it. A book-signing was scheduled in downtown Boston the day before his convention speech.