The e-mail was sent to the newspaper inadvertently by the Republican National Committee, the Tribune said. It recounted a bit from Limbaugh's syndicated radio show in which the conservative talker imagined a conversation between Democratic presidential nominee Barack Obama and Alaska Gov. Sarah Palin, John McCain's choice for running mate.
Palin is anti-abortion and has been praised for carrying her fifth child to term even though she knew the baby would be born with Down syndrome.
Limbaugh's sketch has Obama asking Palin, "When you found out your baby would be born with Down syndrome, did you consider killing it before or after the due date?"
In an internal e-mail, RNC officials discussed using Limbaugh's joke in a YouTube clip.
The RNC issued a statement Saturday saying a "staffer with separate responsibilities made a poor recommendation that was not heeded. The individual has been spoken to and this will not occur again."
The RNC asked the Tribune not to publish the e-mail but the newspaper said the communication illustrated "how campaigns really work and helps to explain why many people think the national political discourse is noxious."