Top Republicans tried Wednesday to figure out how they apparently managed to lose control of Congress after a dozen years of dominating the national political landscape.

"We have to stand on our principles and we will be successful again," said former House Majority Leader Tom Delay, the Texas Republican who resigned in June after being indicted in a campaign-finance scandal. Democrat Nick Lampson won his old seat Tuesday.

"This loss should remind us what we stand for," Delay said. "This country is center-right in terms of its values. We need to show this country that we can take leadership on those principles."

While Republicans try to determine whether voters rejected them because their candidates were too conservative or because the candidates strayed from their conservative values, Democratic leaders expressed satisfaction with a nuts-and-bolts drive to bring their voters to the polls.

That effort spearheaded a 30-seat gain by Democrats in the House. The Democrats also appear to be on the verge of taking control of the Senate.

"It was a thumpin'," President Bush told reporters. The Democratic Party "had a good night."

Democratic National Committee chairman Howard Dean devised a much-criticized effort known as the "50-state strategy." The program coordinated hundreds of organizers for each state party, adding numbers and expertise to often undermanned and underfunded organizations.

It was designed to counter the Republicans' "72-hour program," an effort to target voters and get them to the polls.

Dean blamed the GOP rout on Republicans who put the party's interests "ahead of the interests of the American people. ... The American people were tired of President Bush and his Republican Congress that rubber-stamped his agenda without concern for what was best for America."

Democrats likely will see their more-centrist winners vying with more-left-leaning leaders like Nancy Pelosi, of San Francisco, likely the next House speaker, to determine the party's future, said Donald Kettl, director of the University of Pennsylvania's Fels Institute of Government.

Dean said he does not see the potential for splits between conservative, centrist and leftist Democrats.

"Republicans use labels to divide people, and we're not going to do that," he said. "This election, Democrats united behind an agenda to help all of America's families. It was an agenda to make health care more affordable, raise the minimum wage, help our kids go to college, and to find a new direction in Iraq."

Republican National Committee chairman Ken Mehlman thinks his party didn't push conservative issues and too often ignored unethical behavior. The party was bruised by indictments of congressmen, such as Bob Ney of Ohio and Randy "Duke" Cunningham of California, and the sordid allegations surrounding Mark Foley of Florida.

"This was not a rejection of our ideology. It was, in my opinion, a statement by the American people that we were not doing enough to advance our principles," Mehlman said. "We are not building a common ground with the members of the other side on those principles, and we make a mistake and look the other way if people in our cause and members of our ranks aren't following ethical standards."

As proof, he said most of the congressional seats captured by Democrats "were not won by far-left candidates. It was almost, across the board, conservative Democrats."

One example might be Bob Casey, a pro-life, pro-gun Democrat who trounced U.S. Sen. Rick Santorum, R-Penn Hills. Santorum, the Senate's third-ranking Republican, developed a national reputation on those issues.

"Look," said Mehlman, "the American people sent us a message ... we have got to do a better job as Republicans and as conservatives. We have to recommit ourselves to our core principles, our core mission and our core values" and to "work on a bipartisan basis" when principles allow.

He also called on Republicans "to work, in a way like the Truman Doctrine, that builds a bipartisan strategy for what is going to be a generational struggle" while remaining "the party that is committed to conservative reform."