Stephen Crowley / The New York TimesVice President Joe Biden stands next to Julia Louis-Dreyfus Tuesday at a state dinner in Washington. Friday, Biden spoke candidly about midterm elections and their effects on policy.

WASHINGTON — President Barack Obama’s ambitious trade agenda appeared to fall further victim to election-year politics on Capitol Hill Friday, when Vice President Joe Biden, in a closed-door retreat with House Democrats, said he understood why they would not grant Obama the crucial authority he needs to conclude large trade deals with Asia and Europe.

Biden’s comments most immediately called into question the Trans-Pacific Partnership, a regional pact among 12 nations that would be one of the world’s biggest trade agreements. It is a central element of Obama’s strategic shift toward Asia, and the White House had hoped to complete it last year. Responding to a question at the policy retreat for House Democratic leaders in Cambridge, Md., Biden said he understood that legislation for expedited consideration in Congress for free-trade agreements, known as fast-track authority, was not coming up for a vote now, according to several people who were in the meeting.

Winning that authority is viewed as necessary for Obama to extract politically difficult concessions from Japan, Singapore and other Pacific Rim countries. The Trans-Pacific Partnership aims to reduce tariffs on a vast array of goods and services and to harmonize regulations. It would affect 40 percent of America’s exports and imports.

For Obama, the trade deal would also lend economic substance to a policy on Asia that is otherwise largely about shifting some military forces to the region as a counterweight to a rising China.

But with Democrats facing a difficult midterm election in nine months, Biden appeared sensitive to their more parochial concerns, including the pressures they face from organized labor. He took a hard line against the largest U.S. trading partners in the Pacific and told Democrats, for example, that he had warned the Japanese on a recent trip to Tokyo that the pact could not go forward if the U.S. auto industry continued to have only 1 percent market penetration in Japan.

Many Democrats typically oppose trade deals, along with their allies in unions and environmental and consumer groups, because they do not want to encourage free-trade agreements they say would siphon off manufacturing jobs from the U.S. and create pollution.