Continued from page 2

Population patterns

The Democratic Party also has had to contend with shifting demographics, most notably the defection of many white blue-collar voters to the Republican Party.

“It’s not just because of the president’s health care law, and it’s not just because of the temporary issues that occur from candidate to candidate,” Mr. Rasmussen said. “It has been a fundamental change in the perception of the Democratic Party and the perception of what works for the economy.”

The party’s most loyal supporters, specifically blacks, Hispanics, younger voters and college graduates, still will propel many Democrats to victory in liberal districts nationwide next year.

The heavy concentration of these voters into geographical enclaves — particularly large urban areas and college towns — will make it more difficult for the party to recapture the House anytime soon, said David Wasserman, who covers House races for the Cook Political Report.

“The Democrats’ coalition today is the most geographically inefficient coalition for purposes of winning the House,” he said. “We had this era over the course of the ‘50s all the way through the ‘90s where we mostly had Republican presidents and a Democratic Congress. We may be entering a new era where the roles are kind of reversed.”

This geographical density for Democrats creates a scenario in which, if all the ballots cast in House races nationally were added together and the Democratic Party won the popular vote, they still could lose the House by two dozen seats, Mr. Wasserman said.

“To the extent that Democrats have a wave election year and are able to win the generic ballot by 5 or more [percentage] points, they have a shot at winning the House,” he said. “But in neutral environment or in a pro-Republican environment, it is Republicans who are going to win the House.”

This article is based in part on wire service reports.