The incidents include faxed messages to House Majority Whip Clyburn and Rep. Bart Stupak, D-Mich., that included depictions of a hangman's noose. One fax sent to Clyburn's district office in South Carolina included the misspelled word "n----r," while one to Stupak called him a "baby-killing [expletive]" and another he received directed a racial taunt at President Obama.
Other incidents tied to the vote include a voicemail left at the western New York campaign office of House Rules Chairwoman Louise Slaughter that mentioned snipers and a window at her district office that was broken by a brick; the shattering of a door at the Tucson office of Rep. Gabrielle Giffords, D-Ariz., and the cutting of a gas line at the Charlottesville, Va., home of the brother of Rep. Tom Perriello, D-Va., after critics of the legislation publicized the address.
"This stuff is beyond the pale," said Clyburn, who added that he would not be intimidated.
Stupak, who decided to support the health bill after Obama said he would issue an executive order dealing with a prohibition of abortion funding, said some of the threats he received "are real cause to worry."
Slaughter called the events in her district "very distressing," but said, "it's more disturbing to me that Republican leadership has not condemned these attacks and appears to be fanning the flames with coded rhetoric."
She pointed to Republican National Committee Chairman Michael Steele's claims that Speaker Nancy Pelosi should be "on the firing line," and former GOP vice presidential nominee Sarah Palin's depiction of some House Democratic members' districts in the crosshairs of a rifle scope.
Slaughter noted that the threats and vandalism followed protesters hurling racial slurs and obscenities at Democratic lawmakers outside the Capitol last weekend, and some Republican House members taking to the balcony outside the Speaker's lobby to seemingly encourage the protesters.
Clyburn, too, said Republican lawmakers shared the blame.
"People out there in the streets get their signals or what they think are their signals from the people in positions like we hold and so if we don't disown that and go get our people to move beyond that, if we participate in it, either from the balcony or on the floor of the House, you are aiding and abetting this kind of behavior," Clyburn said on MSNBC.
House Minority Leader John Boehner, who delivered an angry denunciation of the bill before the final vote Sunday night, appealed for calm.
"Violence and threats are unacceptable," he said. "That's not the American way. We need to take that anger and channel it into positive change. Call your congressman, go out and register people to vote, go volunteer on a political campaign, make your voice heard -- but let's do it the right way."
House Majority Leader Steny Hoyer said more than 10 incidents had been cataloged. He spoke after a closed-door meeting at the Capitol that included members of the Democratic Caucus with Shawn Henry, the FBI special agent in charge of the Washington field office, Timothy Durand of the FBI Violent Crimes Task Force, Capitol Police Chief Phillip Morse Sr., and House Sergeant at Arms Bill Livingood.
After the meeting, the FBI released a statement confirming its involvement in the investigation of some of the incidents.
"All threats and incidents directed against members of Congress are taken seriously and are being investigated by the FBI, U.S. Capitol Police and other law enforcement agencies to identify and bring to justice those responsible," the agency said in the statement.