"But there's no evidence of major erosion of Democratic support in marginal districts."

Although the 4th is a marginal district on paper, its configuration makes it very difficult to unseat an incumbent in a normal election year.

"In marginal districts, voting for the repeal could help," particularly in areas where where there are a lot of hunters.

In general these methods are only effective in marginal districts and only affect the allocation of a single seat per district.

"In a lot of these marginal districts, we have no base."

The 53rd was one of several marginal districts to go Republican in that cycle.

"Republican incumbents who are in marginal districts with suburban bases outside the South should be concerned."

"People who thought they were safe will find themselves in marginal districts," Mr. Weprin said.

Land in Grant was visually run-down country, located in marginal districts.

A freshman, he won two years ago by fewer than 5,000 votes in a marginal district, and this year he is running from his party.