CNN reported that the Clinton ad depicts children asleep in their beds in the middle of the night and asks viewers who they would rather have in the White House during a national security crisis.

"It's 3 a.m. and your children are safely asleep. Who do you want answering the phone?" the spot says.

Obama accused Clinton of trying to scare voters.

"We've seen these ads before," the Illinois senator said in Houston. "They're the kind that play on people's fears to scare up votes."

Obama said the United States has, in fact, had such a crisis, when the decision was made for the March 2003 invasion of Iraq. He said Clinton and the Republican front-runner, Arizona Sen. John McCain, were both wrong for voting to give President George W. Bush authority to invade Iraq.

Obama released a similar ad in response to the Clinton ad, The New York Times reported.

"It's 3 a.m. and your children are safe and asleep," the announcer says. "But there's a phone ringing in the White House. Something's happening in the world. When that call gets answered, shouldn't the president be the one -- the only one -- who had judgment and courage to oppose the Iraq war from the start."