It was a rare breach of the protocol that governs ritualistic events in the Capitol. In an angry and very audible outburst, Representative Joe Wilson, Republican of South Carolina, interrupted President Obama’s speech Wednesday night with a shout of “You lie!” reports the New York Times.

His eruption — in response to Mr. Obama’s statement that Democratic health proposals would not cover illegal immigrants — stunned members of both parties in the House chamber.

Democrats said it showed lack of respect for the office of the presidency and was reminiscent of Republican disruptions at recent public forums on health care.

“It is outrageous,” said Representative Joseph Crowley, Democrat of New York, who said it reminded him of the “antics that are being used to disrupt and fog what is going on.”

After the speech, Rahm Emanuel, the White House chief of staff who sat a few rows in front of Mr. Wilson, said he immediately approached senior Republican lawmakers to encourage them to identify the heckler and urge him to issue an apology quickly.

“No president has ever been treated like that. Ever,” Mr. Emanuel said.

Other Democrats said they did not want to dwell on the outburst or allow it to overshadow what they saw as an effective address by the president. But they also said it bolstered their contention that some Republicans were not interested in constructive dialogue, and they noted that Democratic plans specifically barred coverage for illegal immigrants.

Republicans also said the heckling was out of line. “I think we ought to treat the president with respect,” said Senator Mitch McConnell of Kentucky, the Republican leader, “and anything other than that is not appropriate.”

Read more here: In Lawmaker’s Outburst, a Rare Breach of Protocol