GWEN IFILL: It appears that, for today at least, bipartisanship may be alive and well on Capitol Hill. As we reported a few moments ago, top lawmakers from both parties struck a long-sought deal to give the president — to give President Obama the authority to negotiate a sweeping trade pact with Pacific nations.

Here to fill in the picture, NewsHour political editor Lisa Desjardins.

So, they agreed do, as we reported, is allow a yes-or-no vote on this negotiation — on this trade pact.

LISA DESJARDINS: Right.

GWEN IFILL: What is the significance of that?

LISA DESJARDINS: A lot of the viewers might remember fast track authority. That's what this is.

GWEN IFILL: Right.

LISA DESJARDINS: Let me explain this. We can look at a graphic here. Fast track authority means that the president can bring the outlines of a deal to Congress. If it meets the objectives that Congress is setting in the deal today, then the president gets it fast-tracked. He gets an up-or-down vote.

And, Gwen, that's so significant because it means Congress can't amend a trade deal. That's important to all of those Pacific nations and other nations we're negotiating with, who don't want to agree to a deal and then have Congress have the ability to change it. Here, Congress, yes or no.

GWEN IFILL: What is the Trans-Pacific Partnership that the Asian nations are so anxiously waiting on us to act on?

LISA DESJARDINS: This is a very significant trade deal.

The transpacific nations incorporate 40 percent of the world's GDP. These are some of the countries highlighted right here. One of the most important partners in that group is Japan, who, by the way, their prime minister will be here on an eight-day tour in just a couple of weeks. Timing a coincidence? No, not at all.

That's why they want to move this fast track now. They want him to be here and they want to be able to say we are open to this Trans-Pacific Partnership with you, which opens, basically, more doors for trade. There's a debate over whether it's good or bad.

GWEN IFILL: As you know, all politics is local, all politics is domestic.

LISA DESJARDINS: Yes. Yes.

GWEN IFILL: And a lot of Democrats are not happy about this and unions are not happy about this.

LISA DESJARDINS: Yes.

This is fascinating. The president has broken with unions here. Unions think this is a terrible deal. They think it will mean lower wages for their workers here. They think it will mean human rights violations possibly overseas. They also think it could have problems, including the environment. Unions oppose this adamantly.

And, in fact, Gwen, the AFL-CIO told me today they are going to launch ads against particular senators and House members. If this has a weak point on the Hill, it's the House. Right now, the Senate looks like it's behind this agreement generally.

GWEN IFILL: Except for Chuck Schumer, who may be rising in the ranks of the Senate shortly.

LISA DESJARDINS: Thank God you said that. That's right.

Chuck Schumer is the one to watch here, Chuck Schumer, who is the heir-apparent to Harry Reid. He today, in a hearing on this, said he's skeptical about it. And here's what he needs to get on board. They need better currency manipulation protections. They feel that there's no teeth in this deal, that all these Asian countries can just manipulate their currencies and increase trade in their direction.

Schumer wants more currency manipulation protections.

GWEN IFILL: In the blink of an eye, the president came out with a statement supporting this agreement today. What is the significant of a White House endorsement?

LISA DESJARDINS: Oh, I think it's huge. We knew the president liked this, but what was interesting in that statement, Gwen, is, he went out of his way to say: I care about American workers. I think this is good for American workers.

He knows this is a problem for him on the left with unions.

GWEN IFILL: And, at the very least, he can say to President Abe when he comes here, we're working on it — Prime Minister Abe.

LISA DESJARDINS: That's right. That's right.

This is huge for the State Department and also for the trade reps that have been working on this for a long time, and not only on this one, but also other trade deals, one with Europe that is in the works as well.

GWEN IFILL: OK. Well, Lisa Desjardins, as usual, going behind the scenes for us. Thank you.

LISA DESJARDINS: I love it. Thank you.