It will allow the 68-year-old Mr. Foster, a onetime Democrat who has never demonstrated great partisan fealty, to concentrate on his own race without being drawn into down-the-ballot sideshows.

In an age of doggedly temperate politicians, there is something raw and reckless about Rogan, a onetime Democrat turned conservative Republican.

Mr. Specter, a onetime Democrat with one of the most liberal voting records of any Republican in the Senate, has also alienated some of his supporters.

Mr. Johanns, a onetime Democrat who switched parties in the 1980's, received support this year from business groups, farm organizations and some labor unions.

In North Dakota, Governor Hoeven, a former banker and a onetime Democrat, won the office as a Republican in 2000 in his first political campaign.

A onetime Democrat, he switched parties in 1996 and was often described as a more dynamic campaigner than Mr. Humphrey.

Mr. Koch also criticized Mr. Giuliani, a onetime Democrat, for having switched parties and for shifting his position to support abortion rights.

Mr. Bloomberg, a onetime Democrat who became a Republican shortly before running for mayor, has been the chief champion of nonpartisan elections.

But the 61-year-old Senator, a onetime Democrat who was first elected in 1980, says he can already envision the attacks in commercials on his vote on Judge Bork.

Mr. Tauzin, a onetime Democrat who became a Republican in 1995, has a wealth of connections in Congress, where he has served for 24 years.