The Obama administration and other governments that negotiated the nuclear agreement with Iran need to get that deal approved both at the United Nations, and in the legislative bodies of various individual countries.

The P5+1 countries that negotiated the deal plan to get approval from the U.N. first, a move that has outraged many members of the U.S. Congress who say they should get the first shot.

However, the top U.S. negotiator in the Iran nuclear talks said Thursday the U.N. resolution that will be adopted to implement the deal will include a 90-day "review" period that will let Congress and possibly other legislative bodies hold votes on the agreement.

"The way that the UN Security Council resolution is structured, there is an interim period of 60-90 days that I think will accommodate the congressional review," Undersecretary of State for Policy Wendy Sherman told reporters.

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"There may be other legislatures who also want to look at this," she added. "So it anticipates that there is a period of review, while at the same time allowing the international community to speak."

It's not clear that arrangement will satisfy Congress at all. On Thursday, the top Republican and Democrat on the Senate Foreign Relations Committee said Congress should act first.

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For now, however, that's the process, and it's already leading to questions about what would happen if the U.N. approves the deal and the Congress rejects it. It may be a little early to speculate on that, though, as even many Republicans have admitted that it would likely to be difficult for them to stop the deal in Congress.

Here's an outline of how it could all go down:

1) The Obama administration is expected to deliver the agreement to Congress as early as Friday. That would start the clock ticking on a 60-day process for members to review the deal, and possibly vote on whether to approve it or disapprove it.

2) The U.N. will start considering a resolution implementing the agreement next week, and is expected to approve it relatively quickly. Once that happens, the 90-day "review" period for individual governments will begin.

3) Congress may hold hearings on the agreement in August, but is expected to hold votes in September. Under U.S. law, Republicans could call up either a resolution to approve it, or disapprove it, and could also do nothing if they want. Doing nothing would effectively be treated as a default approval from Congress.

An effort to pass a disapproval resolution seems most likely given GOP opposition. Under the law passed earlier this year, only a simple majority would be needed in the House and Senate to send a disapproval bill to President Obama.

One wrinkle here, though, is that in the Senate, 60 votes would be needed to end debate on the bill in a so-called "cloture vote." If Republicans can't find six Democratic senators to agree on cloture (assuming all 54 Republicans vote for it), then the bill will stall in the Senate. If 60 votes are there, the next step would be the final vote, and just 51 senators would be enough to pass the disapproval resolution.

If a disapproval bill stalls in the Senate, it's possible Republicans could try to bring up a resolution approving of the Iran deal, just to show that neither the House nor the Senate could muster the votes to approve it. But that would only be a symbolic move, and would still result in a default approval by Congress.

4) If Congress is able to get a disapproval resolution to Obama, he has said he would veto it, sending it back to both chambers. To override the veto, the House and Senate would have to hold a two-thirds majority vote, a margin that is not expected to be there for opponents of the deal.

In the House, 290 votes would be needed to override Obama's veto. Republicans would need to find 44 Democrats to reach that goal, assuming all 246 Republicans vote to override Obama.

House Minority Leader Nancy Pelosi, D-Calif., said Thursday that she would work hard to get Democrats to support the deal.

In the Senate, 67 votes are needed to override Obama, which means 13 Democrats will be needed if all 54 Republicans vote against Obama.

5) Most agree Congress will either be unable to pass a disapproval resolution, or override Obama's veto. If that's the case, Congress will have run out of its most likely tools for defeating the agreement, and its 60-day review period under U.S. law will end with the deal intact.

6) Soon after, likely in October or November, the U.N.'s 90-day review period will end, and the U.N. resolution implementing will officially be adopted. After that, elements of the agreement take over, including inspections of Iran's nuclear facilities and, if the International Atomic Energy Agency agrees that Iran is in compliance, U.N. sanctions against Iran will start to fall away.