WASHINGTON - President Obama says the "fundamentals" of the 2012 presidential race remain unchanged following a weak debate performance in Denver that rattled his supporters and gave fresh momentum to Republican challenger Mitt Romney.

"Governor Romney had a good night. I had a bad night. It's not the first time I've had a bad night," Obama said in an exclusive conversation with ABC News' Diane Sawyer, his first televised interview since the debate.

Asked by Sawyer whether it was possible his performance had handed the election to Romney, Obama said, "No."

"What's important is the fundamentals of what this race is about haven't changed," he said. "You know, Governor Romney went to a lot of trouble to try to hide what his positions are."

Tune in to "World News with Diane Sawyer" tonight at 6:30pm ET to see the full interview with President Obama

Obama singled out abortion as one of the issues on which Romney has recently and abruptly tried to "cloud" his position.

In an interview with the Des Moines Register on Tuesday, Romney said, "There's no legislation with regards to abortion that I'm familiar with that would become part of my agenda." The comment was a marked shift for the GOP candidate who has pledged during the campaign to advocate support for specific legislation restricting abortion rights.

"This is another example of Governor Romney hiding positions he's been campaigning on for a year and a half," Obama said.

"Is it a lie?" Sawyer asked.

"No, I actually think… when it comes to women's rights to control their own health care decisions, you know, what he has been saying is exactly what he believes," said Obama. "[Romney] thinks that it is appropriate for politicians to inject themselves in those decisions."

Today Governor Romney told reporters, "I think I've said time and again that I'm a pro-life candidate and I'll be a pro-life president."

Americans "won't be fooled by a flailing campaign's manufactured outrage," said spokeswoman Amanda Henneberg of Obama's response to Romney's interview with the Register.