Asked what the party learned in 2018 that could be applied to the 2020 presidential campaign, Tom Perez said "we have to expand the electorate" and "compete everywhere."
Perez says the committee will give guidance on the presidential candidate debate calendar soon and he expects more debates than in 2016.
In Tuesday's election Democrats gained majority control of the House. Data gathered by AP VoteCast, a nationwide survey of 115,000 voters and 22,000 nonvoters, suggest Trump's positions on the courts and border security cost the Republican Party seats.
Perez spoke Thursday at a Christian Science Monitor breakfast.
Trump says Vice President Mike Pence will be his running mate in 2020.
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