In the midst of answering a question about reducing the federal deficit, Perry reminded the audience he had a plan to cut three government agencies immediately upon becoming president. But while he reeled off the Department of Commerce and the Department of Education, he could not remember the third.

"It's fatal," said Tony Fratto, a former White House spokesman for the Bush Administration. "If it happened on its own he may have survived .... but there have been a series of gaffes and this is probably fatal."

Another Republican strategist agreed.

"It was the death knell," said Sara Fagen, former director of political affairs for the Bush Administration. "Perry had the opportunity to re-emerge at this debate...and he squandered that opportunity."

Futures on Perry's candidacy at Intrade, the online trading site that allows futures trading on candidate prospects and other types of bets, immediately took a dive following the blunder (see below).