NAIROBI, Kenya  On Tuesday morning, Jerome R. Corsi was all set to bash Senator Barack Obama on his ancestral soil.

Mr. Corsi, a right-wing author who specializes in attack books, came to Kenya to publicize his newest work, “The Obama Nation,” which raises pointed questions about Mr. Obama’s history of drug use, his “extensive connections” to Islam and his relationships with Kenyan politicians, among other things  allegations that Mr. Obama’s campaign and others have widely disputed.

The chairs and microphone were all set up in one of the biggest hotels in Nairobi, the capital. Many journalists had crowded in to hear what Mr. Corsi would say about Mr. Obama, the Democratic presidential candidate whose father was Kenyan and who is adored here like a native son.

But it was not to be.

A few minutes before Mr. Corsi was to speak, more than 20 Kenyan immigration agents swooped into the hotel and arrested him. He was whisked off to the immigration office, where officials said he had misled them on his entry papers. By the end of the day, Mr. Corsi’s aides said that he was being booted from the country.