Interviews with more than two dozen Democratic members of Congress, state party officials and strategists revealed a new urgency about the need to address the party’s prospects. One Democratic lawmaker, who asked not to be identified, said Mr. Obama was becoming “poisonous” to the party’s candidates. At the same time, Democrats are pressing senior aides to Mr. Obama for help from the political network.

“I’m a prolific fund-raiser, but I can’t compete with somebody who has got 50-some-odd billion dollars,” said Representative Joe Garcia of Florida, a vulnerable first-term member who has already faced more than $500,000 in negative TV ads from third-party conservative groups. “One hopes the cavalry is coming. One hopes the cavalry is coming.”

The gap is yawning. Outside Republican groups have spent about $40 million in this election cycle, compared with just $17 million by Democrats.

When two senior White House officials — Jennifer Palmieri, the communications director, and Phil Schiliro, the health care adviser — went to the Capitol late last month to address Senate Democrats about the Affordable Care Act, they were met with angry questions about why Mr. Obama’s well-funded advocacy group, Organizing for Action, was not airing commercials offering them cover on the health law.