To that end, the White House is pushing for congressional authorization to use military force. Multiple sources on Capitol Hill tell the NewsHour they expect the formal request to arrive tomorrow.

　　For more on what the White House wants and why, and how lawmakers are responding to its efforts to win support, I'm joined by chief foreign affairs correspondent Margaret Warner and NewsHour political editor Lisa Desjardins.

　　Welcome back to you both.

　　So, Margaret, why, first of all, is the administration doing this? They have been conducting a campaign against the Islamic State for months.

　　MARGARET WARNER: Absolutely, Judy.

　　And they have been doing it, though, under these AUMFs, one in '01 to justify the war against al-Qaida, and number two to justify the invasion of Iraq. But the president has been thinking about this for a long time. He gave a speech in May of 2013 at National Defense University in which he basically warned this was too open-ended, too outmoded, and could be used by any future president to justify enhanced powers that he felt were inappropriate.

　　So, one, it's sort of deeply felt by him, but, two, there are practical reasons. He wants now bipartisan congressional buy-in for both domestic reasons, when he comes in for funding requests and so on, but also for international reason, to send a message to allies and enemies alike that the American public is really behind this, this isn't just a president going off and doing what he wants here, and that they're in for a long fight.

　　JUDY WOODRUFF: So, what have you been able to learn about the language? What's in this request?

　　MARGARET WARNER: Now, I first have to say, we keep both being warned that this could still change before it's introduced.

　　But it's designed, as one Democratic staffer to me, to thread the needle. Because he wants a bipartisan bill, he has to come up with ways to get Republican buy-in, as well as Democratic, even he has to lose extremes on either end. So, what we're told today is, one, there are restrictions on the use of ground forces, that it barred enduring offensive ground operations.

　　That was the language as of the middle of the day. There are a lot of exemptions, special forces, advisers and trainers, the 3,000 that are already on the ground in Iraq. Two, it would sunset in three years, so any future president would have to return for new authorization.

　　And, three, it repeals one of the old AUMFs, the one used to justify going into Iraq, but not the original 2001 against Iraq. And that's one in which the Democrats wanted to repeal both and the Republicans didn't want to repeal either.

　　JUDY WOODRUFF: So, you have been talking — there's a lot to with here, Lisa. You have been talking to people on Capitol Hill. What kind of reception is this going to get?

　　LISA DESJARDINS: Margaret said the president has been thinking about this a long time. Members of Congress have been thinking about this a lot for a long time.

　　There's positive reception, in that the president has sent this authorization request up, even though he technically doesn't have to, or at least logistically doesn't have to. It's sort of an acknowledgement of the power of Congress. That's appreciated obviously in the split power that we have right now.

　　However, Judy, there's a lot of caution. People want to see the exact wording, because while you can say that the president has signaled, we have both been hearing from our sources, that he's going to restrict ground troops in this authorization, the wording matters so much. And that's what members of Congress, especially Republicans, are waiting to see.

　　But what's interesting overall here is, this is a bipartisan plan. It splits both parties. That's risky, or it could be brilliant. We will see what happens with the votes.

　　JUDY WOODRUFF: So what it is coming down to? Is the ground troop — boots on the ground language the most important piece of this? Is it the duration of the agreement? What is it that members are arguing?

　　LISA DESJARDINS: There are many working parts. The ground troop component is crucial, especially for Democrats. That might bring a lot of Democrats on if they believe it is a truly firm restriction.

　　If it doesn't, he may lose the more liberal wing of the Democratic Party. But there's something else that people are talking about. They're talking about, what are the geographic parameters? What exactly does this limit in terms of geography? The old Iraq war powers resolution was specific to Iraq for the most part.

　　Well, the Islamic State is something that goes beyond borders. How will the president deal with that in this resolution? So we're talking about completely changing our approach to not just Iraq, but to a much broader territory. That's why language matters.

　　JUDY WOODRUFF: So, tell us about that.

　　MARGARET WARNER: Yes.

　　So, Senator Kerry last December — there was an earlier version of this, which I won't get into. But he made an impassioned statement in front of a Senate committee saying, no geographic limits. And there are no geographic limits in this specifically set. Now, it doesn't mean it will survive, because, Senator Corker's people are saying and Senator Corker said, as far as we're concerned, this is just the starting point. We are going to have hearings and we want the president to stay engaged.

　　LISA DESJARDINS: Right.

　　MARGARET WARNER: We want him to explain the strategy on Syria, which both a leading Democrat, Tim Kaine, and Senator Corker think has not been laid out.

　　And the administration knows if they put this forward, which they are going to, they can't risk the fiasco that happened back a year-and-a-half ago, where he said, remember, I'm going to go to Congress for authorization to strike Syria over chemical weapons. And then everyone — he kind of wimped out. And that really damaged perception of American leadership in the world, the administration knows.

　　JUDY WOODRUFF: So, Lisa, it sounds like they're still sorting this out on the Hill. It's not clear where the lines are going to be drawn.

　　LISA DESJARDINS: That's right.

　　And I think the White House knows that. So, they have been — it's not the slowest of rolls, but it's a bit of a slow roll. That's — tomorrow, we know that House — that Senate Republicans are going to meet at 5:00 as a group.

　　And that indicates the seriousness of this. There are heavy politics involved here, but there is also a sense on Capitol Hill that this is a very important national matter. They meet tomorrow. Everyone in Congress goes home next week. Then we will see in the following weeks.

　　In general, I'm being told by my sources, expect this to take months of debate, more than weeks.

　　JUDY WOODRUFF: And, Margaret, is the White House sounding confident, not sure? What's your read?

　　MARGARET WARNER: Well, they're sounding confident that their outreach has been successful.

　　And you heard Senator John Cornyn, Republican of Texas, no fan of the White House, actually say today that he thought — he appreciated the outreach. So I think that the Congress knows that the president is taking them seriously and the White House is putting a lot of stock in that.

　　But, from talking to people on the Hill, I think they are going to have a lot to explain and a lot to answer for when they actually go up there and testify.

　　LISA DESJARDINS: He needs 60 votes. Tough.

　　JUDY WOODRUFF: It's not 51. Sixty is a matter…

　　LISA DESJARDINS: Right.

　　JUDY WOODRUFF: Well, assuming it does come out tomorrow, and we do, we will certainly be looking at it in greater length tomorrow.

　　Lisa Desjardins, Margaret Warner, thank you both.

　　LISA DESJARDINS: My pleasure. Thank you.