Jeffrey Lord, the indefatigable defender of President Trump whose advocacy turned him into an unlikely political celebrity, was fired by CNN on Thursday after a convoluted Twitter exchange in which he evoked — mockingly, he said — a Nazi salute.

Mr. Lord received the news by telephone while on his way to CNN’s Manhattan studio in a town car provided by the network, which ferried him from his home near Harrisburg, Pa.

After Mr. Lord, 66, learned that his contract had been severed, the car turned around. “I didn’t have to walk; I thanked them for that,” he said in a telephone interview from the road.

While Mr. Lord was often castigated by critics for his relentless lobbying on Mr. Trump’s behalf — he was once rebuked on air by Anderson Cooper in particularly crude terms — it was a social media squabble that led to his ouster.