Start with president obama and his stunning decision to put what appeared to be an imminent attack on syria on hold. Now looking to congress to approve military action, after britain, a key u.S. Ally... See More
Start with president obama and his stunning decision to put what appeared to be an imminent attack on syria on hold. Now looking to congress to approve military action, after britain, a key u.S. Ally backed out. This delays it for a week, because congress is out of session until september 9 president we begin with jonathan cart from the white house. Quite a surprising turn of events. Absolutely. The president has told the world he believes the united states should launch a military attack against syria. He also made it clear he's not ready to act alone. The president made a indication that the syrian government must be punished for using chemical weapons. I have decided that the united states should take military action against syrian regime targets. It's not open-ended. But I'm confident we can hold them accountable for the use of chemical weapons, deter the behavior, and degrade their capacity to carry it out. Reporter: But he isn't ready to launch an attack yet. He wants to get a green light from congress. While I believe I have the authority to carry out this military action without specific authorization, the country will be stronger if we do this. Reporter: It will delay action by two weeks or more, but the president said he has time. Our capacity to execute is not time sensitive. It will be effective tomorrow or next week or one month from now. And I'm prepared to give that order. Reporter: It was the president more than a year ago warned syria -- a red line for us is a whole bunch of chemical weapons moving around or utilized. Now that they've done it, america must act. We do what we say, and we lead in the belief that right makes might. Not the other way around. Reporter: He will attempt to build especially support beginning with russia this week for a submit meeting of world leaders, including several that are opposed to the military strike. And that includes the president of russia, an interesting interaction. No question. Thank you for your reporting. Now the action from the white house to capitol hill where the administration is going to launch an all-out lobbying campaign, and lawmakers have started to grapple with a major decision. Abc news jeff is at the capital. Walk us through the order of operations. When does the debate start? Reporter: Good morning. The debate is not going to start officially until next week. Congress is on the week long recess, finishing up the summer break. The votes start next week. But there's a classified briefing on the hill this afternoon. The senate foreign relation committee starts taking witness testimony on tuesday. This is the critical week that the white house has to explain its position, makes it case to congress. Right now I'm told by senior officials on both sides, the votes are not there yet. The white house has work to do over the we. What's your sense of whether it will pass? The whole world was surprised when the britain parliament voted against this. What are the odds here in the u.S. Congress? Reporter: The odds in the u.S. Congress are right now if this vote was taken today, I'm told by lawmakers on both sides, it would not pass. But as always, things can change. But if it were to pass, it would have to be unusual alliance of democrats and republicans. Some libertarians and liberals are opposed. It's threatening a difficult needle. A huge gamble. Thank you. Let's bring in george stephanopoulos who is the host of "this week." Let me ask this question -- let me put up a picture as I ask the question. This is the situation room on friday night, the president and the national security team. Look at the faces. Everybody so grim as they make the decision. As I look, let's ask, if the votes go against them, will they act anyway? He would be the first president in modern times to lose a vote on military force. That was the question that president obama ignored when he left the rose garden yesterday. That was the question being shouted out. I'm going to ask secretary of state kerry this morning. They don't have a choice. Even if they lose, the president given what he said about the scale of the crime, a crime against humanity, he will have to act. He will be doing it without congressional authorization. To bet the white house and the president this is going to pass, and strengthen his hand. Why not call congress back sooner? Did the president box himself in by drawing that red line with chemical weapons? That is the big question. If you look a year ago, a lot of people were surprised with the red line. On the other hand, when you look at the scale of the attack, it would have been hard to ignore. I talked to white house officials why they didn't call them back earlier. That is the decision. One of the other things he said yesterday is the chairman of the joint chiefs of staff told him it doesn't matter. Whenever he gives the order, they will carry out the mission. A couple weeks doesn't matter. Ing interesting to see that. And on "this week," he will be going one-on-one with the secretary of state john kerry. Thank you.
This transcript has been automatically generated and may not be 100% accurate.