Barack Obama's not the first president to run for re-election in tough times. As he accepts his party's nomination on Sept. 6, perhaps he'll take inspiration from history.

Four years ago at the 2008 Democratic Convention in Denver, then-Sen. Barack Obama was a rock star. His speech about hope, change and the future brought thousands of voters to their feet and millions to the polls.

"Tonight, I say to the American people, to Democrats and Republicans and Independents across this great land: enough! This moment — this election — is our chance to keep, in the 21st century, the American promise alive."

Tom Whalen, a Boston University presidential historian, says Obama has a tougher job this time around. "It’s like a marriage. Is anyone as excited about each other the same way they were going into a honeymoon night? No, I don’t think so."

So what does President Obama have to say to convince the American people to give the marriage another shot?

For pointers, Whalen says Obama can look to Franklin Roosevelt's speech at the 1936 Democratic Convention. In 1936, FDR was coming out of a first term where he accomplished many things, but even though his policies were able to relieve some of the suffering, they did not get the economy out of the Great Depression.

“What he told Americans in 1936 was, ‘We have a long road to go but you know what, I’ve kept my part of the bargain. I’ve done what I can to improve the situation, in that if we just follow my leadership and my policies, we’ll truly get out of this mess,'" Whalen says. "And he told Americans that he and they had a rendezvous with destiny, a better destiny than what the Great Depression had dealt them and the previous Republican administration."

In the speech, Roosevelt also painted the reason why things weren’t better. He said it had to do with what he called the "economic royalists" in this country”: the big businessmen who were not willing to sacrifice for the common good.

"Through new uses of corporations, banks and securities, new machinery of industry and agriculture, of labor and capital — all undreamed of by the Fathers — the whole structure of modern life was impressed into this royal service,” he said.

Whalen says Obama can say something similar. "I think President Obama, and he made use of it up to this point, will make similar kinds of statements. That 'I’m in it for a long haul but we have a lot of people — big-shot, fat-cat, billionaire types — who want to make a short-term profit. The hell with everyone else.’"

Whalen says Obama, like Roosevelt, needs to give voters confidence that his plans to improve the economy are working and things will get better in a second term.

Whalen says perhaps that will be enough to make the base fall in love with the President all over again.