"If the Democrats ... squander the opportunity that we've been given over the next two years, we'll have problems in '08," he told reporters before speaking to a UNITY: Journalist of Color Inc. reception to kick off the group's plans for a 2008 national convention in Chicago.
Obama said it's not enough for Democrats, who will control both the House and Senate for the first time since 1994, to just run against President Bush.
"We're going to have to make progress," said Obama, who stumped for Democrats nationwide and was among his party's best fundraisers leading up the election.
The freshman senator said the question is whether the president is willing to engage in bipartisan talks about issues like Iraq and budget and ethics reforms. If he is, Obama said Democrats need to negotiate with him on all those issues.
"The American people — they don't want payback, they want progress," Obama said.
While Obama said he believed Tuesday's election signaled the degree to which Americans are looking for something new from Washington, he still has not answered the main question looming around him: will he run for president in 2008?
He did say Thursday that he will have to make a decision over the next "several months."
Iowa Gov. Tom Vilsack on Thursday became the first Democrat to formally announce a 2008 bid, filing documents with the Federal Election Commission.
Obama said other candidates won't factor into his decision.
"The one thing I won't think about is who else is running," he said.
Obama also spoke to CBS station WBBM in Chicago about the death Thursday of veteran CBS newsman Ed Bradley.
"Ed and I had the opportunity to meet while I was on the campaign trail. I had been a fan of his for a long time," Obama said.
"I think he embodied class, he was a tough journalist, but fair, and set the standard not just for African-American journalists, but for journalists generally. He will be missed."