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

Mr. 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 Mr. 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., Mr. 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 Mr. 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 Mr. 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.