GOP presidential candidate Rick Perry reads the “Top Ten” list on the “Late Show with David Letterman” on Thursday.

WASHINGTON — “Sorry. Oops,” Texas Gov. Rick Perry said Wednesday night when pressed during a Republican presidential debate to name the third federal agency he would eliminate if he won the White House.

“Commerce, Education and the — what’s the third one there? Let’s see,” said Perry, who has repeated the trio of agencies on the campaign trail innumerable times.

This wasn’t the first such misstep for Perry — and it joins a long history of gaffes during televised debates that have become a central and unforgiving element of modern American presidential campaigns.

For Perry, the mistake may be fatal to his presidential hopes, said Susan Tolchin, a public policy professor at George Mason University in Fairfax, Va.

The lapse in remembering the Energy Department for Perry, the governor of a top energy-producing state, “really rendered him toast in this campaign,” she said in an interview.

“It looked like, without a teleprompter, he was lost.”

Televised debates have helped shape public perceptions of presidential candidates since their 1960 debut.

For many listening to that debate on the radio, Vice President Richard Nixon, the Republican candidate, was the winner.

Those watching on television, however, saw Nixon appearing unshaven, uncomfortable and sweating. To them, his more telegenic opponent, Massachusetts Senator John F. Kennedy, had the edge, Tolchin said.

In 1976, during a debate with Democratic challenger Jimmy Carter, President Gerald Ford slipped in describing the Soviet Union’s influence over Eastern European nations in its bloc.

“There is no Soviet domination of Eastern Europe, and there never will be under a Ford administration,” Ford said. “Each of those countries is independent, autonomous.”

In 1988, Democratic candidate Michael Dukakis, the Massachusetts governor and a longtime opponent of capital punishment, was asked whether he would support the death penalty if his wife were raped and murdered.

“I don’t see any evidence it’s a deterrent, and I think there are better and more effective ways to deal with violent crime,” he replied.

That response confirmed for many voters that Dukakis was a technocrat detached from emotion, said Leonard Steinhorn, a communications professor at American University in Washington who was a volunteer speech-writer for the governor’s campaign.

“Dukakis’ answer was somewhat cold and bloodless,” Steinhorn said in an interview.

Vice presidential candidates also have “stepped in it,” as Perry characterized his debate performance today on NBC’s “Today” program.

In 1992, retired Admiral James Stockdale, running with businessman Ross Perot on a third-party ticket, said during a debate with his counterparts, “Who am I? Why am I here?”

Voters had the same questions, and Perot and Stockdale were outrun by Democrats Bill Clinton and Al Gore.

In a 1988 debate, Republican vice presidential candidate Dan Quayle, an Indiana senator running with George H.W. Bush, said he had “as much experience as Jack Kennedy” did before Kennedy ran for president.

Quayle’s Democratic rival, Lloyd Bentsen, pounced.

“Senator, I served with Jack Kennedy, I knew Jack Kennedy. Jack Kennedy was a friend of mine. Senator, you’re no Jack Kennedy,” said Bentsen, a longtime Texas senator.

Bloopers haven’t always defined candidacies or killed careers. Americans’ concerns with Quayle’s qualifications didn’t prevent the election of the Republican ticket.

Four years earlier, after a lackluster performance in a debate that raised concerns about his age, President Ronald Reagan in a rematch turned the point in his favor against his Democratic challenger, former Vice President Walter Mondale.

“I am not going to exploit for political purposes my opponent’s youth and inexperience,” he said to laughter from the audience — and from his opponent.

Perry’s stumble last night was substantial, Tolchin said.

“That’s a significant thing to forget,” she said. “He could be somebody brand new and he’d be in great trouble.”