“Clint, my hero, is coming across as sad and pathetic,” tweeted film critic Roger Ebert as Eastwood ad-libbed Thursday night to an audience of millions — and one empty chair — on stage at the Republican National Convention. “He didn’t need to do this to himself. It’s unworthy of him.”

Eastwood carried on a long-winded conversation with an imaginary President Barack Obama, telling him that he failed to deliver on his promise and that it’s time for Romney and running mate Paul Ryan to take over.

“Mr. President, how do you handle promises that you have made when you were running for election, and how do you handle them? I mean, what do you say to people?” he said at one point to the empty chair.

Twitter was instantly ablaze with comments mocking the Oscar-winning director of “Unforgiven” and “Million Dollar Baby.”

“Clint has now eclipsed the total word count of his last three films,” tweeted film critic Richard Roeper during the speech, which was intended to last five minutes but went on for nearly 12.

Howard Kurtz, host of CNN’s “Reliable Sources,” said “Clint’s empty chair act” was the “weirdest convention moment I have ever seen.” Joe Scarborough, the conservative host of MSNBC’s “Morning Joe,” declared that “a great night for Mitt Romney just got sidetracked by Clint Eastwood.”

Minutes after Eastwood began his speech, someone created an (at)InvisibleObama account on Twitter. It has already amassed 30,000 followers and counting.

“I heard that Clint Eastwood was channeling me at the RNC,” tweeted comic actor Bob Newhart, known for his one-sided conversation bits. “My lawyers and I are drafting our lawsuit.”

The 82-year-old actor and director, a fiscal conservative who takes left-leaning stands on social issues, also talked about Oprah Winfrey, Obama’s unfulfilled promise to close the U.S. prison at Guantanamo, the wars in Iraq and Afghanistan and lawyers.

“When somebody doesn’t do the job, you gotta let ‘em go,” Eastwood said. The tough-guy actor of “Dirty Harry” fame then drew a finger across his throat.

The Obama campaign shot back afterward by tweeting a photo of the back of the president’s chair, with Obama’s head peeking over it, along with the line: “This seat’s taken.”

A top Obama adviser, David Axelrod, told MSNBC that Republicans must be regretting Eastwood’s rambling speech.

Inside the convention, the crowd cheered the actor’s entrance and shouted his famed catchphrase, “Go ahead, make my day.” But backstage, stern-faced Romney aides winced at times as Eastwood’s remarks stretched on.

After his speech, Romney’s camp defended Eastwood.

“He’s an American icon,” Romney spokeswoman Gail Gitcho told CNN’s Piers Morgan. “You can’t look at him at through the same political lens that you would other politicians. He’s Clint Eastwood.”

Romney’s wife, Ann, was peppered with questions on morning news shows about whether Eastwood’s appearance was a distraction. She said Eastwood is “a unique guy and he did a unique thing last night.”

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Follow AP Entertainment Writer Derrik J. Lang on Twitter at http://www.twitter.com/derrikjlang.

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Associated Press writers Donna Cassata, Kasie Hunt, Steve Peoples and Philip Elliott in Tampa, Florida, and Leanne Italie in New York contributed to this report.