I am an attorney, and have been for more than 30 years, and can give you a very clear answer.
1. Based on several Supreme Court cases that were issued in the 1960s and 1970s, the law of slander and defamation were changed, in order to make sure that people and media have freedom to say what they want in matters of public debate, without fear of getting sued. These cases stemmed from the special status given under the Bill of Rights to Freedom of Speech (including freedom of political association) and Freedom of the Press (which includes of course all news media, and not just newspapers). In order to protect these freedoms, the Court created a special class of person, called a "public figure." A pubic figure is anyone who intentionally or unintentionally is thrust into the realm of public matters or public commentary, whether through politics, fame, or position. It includes politicians, movie stars, members of the school board, and anybody else who is famous or in the public eye.
2. If a person is a Public Figure (and clearly, all people running for public office are), then they cannot sue for slander or defamation merely because statements are false or defaming. They must prove "actual malice", which the courts have defined as follows: They must prove that (i) the statements are absolutely false, (ii) the statements are such that an ordinary person would consider them materially damaging to the business or personal reputation of the victim, (iii) the person or entity making the statements absolutely and positively knew they were false statements when they made or published them, (iv) the person making or publishing the statements went ahead and did it with actual intent of harming the victim, and (v) the statements resulted in actual money damages to the victim. The victim of the slander or defamation has the burden of proving each and every one of these factors, in a court of law, with the cased tried by a jury, in order to recover a single penny. Even then, the jury can decide to issue nominal damages, of say $1.00.
So, in short, based on the Bill of Rights, it is almost impossible for a public figure to ever sue for slander or defamation and win anything. One of the few people who was sucessful at this in recent times, is Carol Burnett, who sued the National Enquirer for falsely reporting that she was drunk at lunch in a famous Hollywood restaurant. She hired the best attorneys in L.A., and pursued them for years, finally winning more than a million dollars in a jury trial, which she immediately donated to charity.
Hope this helps.
Mannyrock