Beneath a headline which included a racial epithet referring to African-Americans, the one-page cartoon showed two L-shaped lynching posts with "Sheila Jackson Lee" written on one cross bar and "Hussein Obama" written on the second cross bar. The president's full name is Barack Hussein Obama.

The return address on the fax said: "Defecating on Obama."

"We are aware of the cartoon, and we are taking appropriate measures," said Secret Service Special Agent Robert Novy, a spokesman for the agency. "Being a protective intelligence matter, the Secret Service has no further comment."

Jackson Lee said she received the cartoon in her congressional office in Houston.

"We have gotten this sort of thing on a regular basis in the past, but I thought this had a heightened level of provocativeness," she said.

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Glenn Rushing, Jackson Lee's chief of staff, said the cartoon arrived by fax in the district office on Saturday - a day after the congresswoman delivered remarks on the House floor questioning whether Republicans were showing "disrespect" toward the president during debt-deficit negotiations because of his race.

Rushing said he referred copies of the threatening pictorial to the House sergeant at arms, former U.S. Secret Service Agent Wilson "Bill" Livingood; U.S. Secret Service Director Mark Sullivan; and FBI Director Robert Mueller.

Jackson Lee defended her remarks on the House floor on Friday in which she questioned "the maligning and maliciousness (toward) this president" by Republicans during hard-nosed negotiations over raising the federal debt ceiling.

"Why is this president being treated so disrespectfully?" asked Jackson Lee, a member of the Congressional Black Caucus. "I am particularly sensitive to the fact that only this president - only this one, only this one - has received the kind of attacks and disagreement and inability to work, only this one. Read between the lines."

stewart.powell@chron.com