Jan, 3, 2008 -- Iowa Democrats received a new round of anonymous phone calls this week, under the guise of opinion poll research, slamming former Sen. John Edwards and Sen. Barack Obama, in the latest display of the ugly side of this year's presidential campaign.
Even before the first vote is cast, 2008 is being called "one of the dirtiest campaigns in American history" by a political science professor who is tracking campaign dirty tricks and opposition research attacks on rival candidates.
"When you're spending this much money, and there's this much at stake, you're going to have dirty tricks played," says Larry Sabato, director of the Center for Politics at the University of Virginia, in an interview for a "20/20" report.
The negative phone calls are known by experts as push poll calls because they push negative information.
"Some foreign policy experts say that John Edwards' plan to pull out all combat troops in Iraq within the next 10 months is irresponsible," says the questioner. "Does this statement influence your feeling about John Edwards a lot, somewhat, not too much, or not at all?"
On Obama, the caller says, "Barack Obama has taken millions of dollars from big banking and energy interests that have legislation before the Senate. Does this influence your feeling about Barack Obama a lot, somewhat, not too much, or not at all?"
The caller said the calls were coming from an "independent research firm." The caller ID showed no return number, only 000-000-0000.
The call made no reference to Sen. Hillary Clinton, whose campaign spokesman "categorically denied" it had any connection to the Clinton campaign.
"It was actually kind of sneaky the way they were worded," said Des Moines schoolteacher Shari Baeth, who recorded the calls for "20/20."
She says the most recent negative call, and another one earlier that favored Edwards (whose campaign also denies using push polls), convinced her to support Obama at the caucus tonight.
"Of the top three, he's the only one I've not received those calls from," she told "20/20."
Republicans have been just as vicious in going after each other with negative and anonymous attacks.
Over the holidays, someone played a dirty trick on candidate Mitt Romney by sending out a Christmas card to South Carolina voters, supposedly from him and his family, extolling the virtues of a "plurality of wives" in the Mormon religion.
Romney denounced the bogus card which carried a Boston postmark.
"It's a very dirty tactic; it's a very dirt piece of literature," said Professor Sabato. "I would think potentially that could be prosecuted; that's misrepresentation on a very serious matter in a campaign," he said.