April 26, 2007  -- Sen. John McCain, who officially announced his bid for the 2008 White House Wednesday, stopped by "Good Morning America" to talk about his campaign and ended up defending himself about a joke.

The Arizona Republican said that people upset by his comments about IEDs to Jon Stewart on Tuesday night's "Daily Show" should "lighten up." After being grilled by Stewart , McCain jokingly told him that he had a present for him -- an IED that he could place under his desk.

Rep. John Murtha, D-Pa., was furious and publicly assailed McCain on the House floor.

"Imagine a presidential candidate making a joke about IEDs when our kids are getting blown up," he said.

Responding to Murtha's reaction, McCain said that he was going to use comedy during his campaign, just as he did during his military duty.

"I don't know how to react to that kind of hysteria to a comedy show," he told Diane Sawyer on "GMA." "All I'm going to say to Murtha and others. … Lighten up and get a life."

On Wednesday, the same day that McCain announced his presidential run, 218 members of the House voted for a bill that contained a troop withdrawal timetable. McCain said that he would rather lose the election than abandon the conviction that a troop withdrawal from Iraq was a bad idea.

"Everything that I know. … That I've learned about my life … dictates that would be a disaster," he said today. "That opinion is shared by most national security experts."

When asked what he would do differently than the Bush administration, McCain said, "I would certainly go to the American people and explain to them what's at stake. … I do know that I don't need on-the-job training."