Could the public sue a Madonna for equal time at her show that she is using to make a political endorsement?

According to news reports, Madonna is using her show to portray McCain with Hitler and Obama with Gandhi. I find this inflammatory, slanderous, and morally corrupt. I am old enough to know how evil Hitler and how good Gandhi was to the world. I know Madonna is old enough to know the difference too, but my best guess is she is using this as a vehicle to sell her albums and concert tickets. Neither McCain nor Obama deserves to be ociated with her characterizations of them. Dixie Chicks move over because Madonna has taken your place infamy.