With only the Iowa caucuses behind it, the 2008 race for the White House is turning out to be "one of the dirtiest campaigns in American history," according to some political experts.
Shari Baeth, a schoolteacher in Des Moines, Iowa, caught one dirty campaign trick -- what's called a push poll -- on tape for "20/20." Push-poll phone calls are made by anonymous callers who push negative information on voters under the guise of opinion polls.
Listen to part of the call here. (ABC News)