After a week of intense bombing of Libyan ground forces and anti-aircraft installations, the president laid out his reasons for going in.
"When our interests and values are at stake, we have a responsibility to act. That's what's happened in Libya," said Obama.
The president said the bombing of Gadhafi's forces has prevented a slaughter in the Libyan city of Bengaszi.
"Gadhafi declared that he would show no mercy to his own people, he compared them to rats, and threatened to go door-to-door to inflict punishment," said Obama.
The president said he knows America cannot intercede in every place where repression occurs and added, "But that cannot be an argument for never acting on behalf of what's right."
In Libya, the president said the U.S. had an international mandate for action, a broad coalition, the support of Arab countries, and a plea from the Libyan people.
"And as president, I refuse to wait for the images of slaughter and mass graves before taking action," said Obama.
The president said he will keep working politically to remove Gadhafi from power, but the military mission does not include regime change and he added NATO will take over the lead on the military action this Wednesday.
House Minority Leader Nancy Pelosi, D-California, stood by the president's action.
"I think the president was courageous in doing that. I think it accomplished its goals, saved tens of thousands of lives," said Pelosi. She said members of Congress are concerned, but the president had to act. "To do nothing in a case where a man is on a path of 'show no mercy' is not to remain neutral."
But Rep. Jackie Speier, D-Hillsborough, said the president should've told Congress how long and what the end game would be before going in.
"This has the fingerprints of an Afghanistan all over again," said Speier.
Rep. Anna Eshoo, D-Palo Alto, isn't ready to condemn the president's action, but she has questions.
"Are we there to support the rebels? Who are the rebels and what exactly is going to be the aftermath? I think the aftermath can't be answered because it's very complicated," said Eshoo.
This Wednesday, members of Congress will get a classified briefing from the Obama administration on the future of US involvement in Libya.