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Representative Jerrold Nadler, the chairman of the House Judiciary Committee, was taken to a hospital after apparently fainting during a news conference on Friday in Manhattan.

Mr. Nadler, 71, was seated at a table in a gymnasium at Public School 199 on the Upper West Side, where Mayor Bill de Blasio was heralding the expansion of New York City’s speed camera program.

Thirty minutes after Mr. Nadler, a Democrat of Manhattan, made brief remarks, his head appeared to slump. A woman seated behind Mr. Nadler pointed at him, and then Mr. de Blasio attempted to revive him as spectators became alarmed.

“It looked like he had just taken a little nap for a moment, and then I put my hand on his shoulder and I said, ‘Jerry are you O.K.?’” Mr. de Blasio said afterward.