WASHINGTON - Democrats said the main lesson of the November election is simple: Go big on the economy.

Party officials attending a daylong conference Wednesday hosted by the Center for American Progress said Democrats failed to make a forceful pitch to middle-class voters on issues like economic opportunity, stagnant wages and rising college costs - and suffered the consequences.

"Too many Democrats did not offer a progressive vision, particularly around economic issues," said New York Mayor Bill de Blasio, pointing to his successful 2013 mayoral campaign as a model. "This year, around the country, I think there was an unwillingness on the part of so many candidates to bluntly define the problem and say, 'Here are the potential solutions.'"

The mayor said the election should serve as a "cautionary tale" as the party prepares for 2016 on the need for a "clear, blunt aggressive economic message."

Headlined by Massachusetts Sen. Elizabeth Warren, the conference followed an Election Day drubbing for Democrats, who surrendered control of the Senate and lost ground to Republicans across the nation. Democrats have said too many candidates distanced themselves from President Barack Obama, who is unpopular in many regions, and ran campaigns that targeted specific voters like women, Latinos and young people but lacked a coherent message on the economy.

"Not standing up for the things you believe in is not really a good idea," said Tom Steyer, a California billionaire who spent millions in support of environmental causes.

Democrats said the party should have emphasized economic issues that would resonate with struggling voters, including spending more money to build roads and bridges, promoting early childhood education and raising taxes on the wealthy.

The lessons could inform how the party competes in the 2016 presidential campaign to succeed Obama. Hillary Rodham Clinton remains the leading Democratic candidate if she decides to run, but many liberals remain skeptical of her willingness to curb Wall Street excess.

Warren, who has denied interest in a presidential campaign, offered her familiar critique that the political system was "rigged" by wealthy interests at the expense of working-class families. But she also gave a pessimistic outlook on the nation's politics during Obama's second term and urged a renewed push for education funding, raising the minimum wage and closing corporate tax loopholes.

"Our country is headed in the wrong direction. The American Dream is slipping out of reach," Warren said.

"We did a horrible job as progressives with connecting with voters on these issues because we are too tentative," said Nick Hanauer, a Seattle-based entrepreneur and venture capitalist. "We haven't advanced an alternative theory of growth. Until we do, we are going to continue to get our butts kicked."