WASHINGTON (AP) -- Congressional proceedings are routinely convoluted, often inscrutable and sometimes bizarre. Even by those standards, the upcoming vote on the Iran nuclear deal stands out as particularly bewildering.

It's a situation, by design, where the Democratic minority will rule the Republican majority.

The winners of the initial vote will end up the losers.

And President Barack Obama stands to be repudiated by at least one chamber of Congress on his top foreign policy priority - yet will emerge triumphant in the end.

A guide to a peculiarly only-in-Washington spectacle, coming this week to the floor of the House and Senate.

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WHAT'S THE DEAL?

At issue is the agreement signed in July by the U.S., Iran and five world powers: China, France, Russia, Britain and Germany. The accord will provide Iran hundreds of billions of dollars in relief from international sanctions in exchange for a decade of constraints on the country's nuclear program.

The deal is unanimously opposed by congressional Republicans and by the leaders of Israel, who fear a newly enriched Iran could wreak havoc across the Middle East. The White House strongly supports it; so do most Democrats, though in some cases reluctantly.

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TAKE THAT, EXECUTIVE BRANCH

The White House first tried to cut the deal without getting Congress involved, viewing it as an executive branch agreement, rather than a formal treaty requiring approval by two-thirds of the Senate.

That did not go over well with lawmakers of either party.

After much debate and controversy, the House and the Senate in May overwhelmingly passed the Iran Nuclear Agreement Review Act, giving Congress the opportunity to review the deal and enact a resolution of disapproval that would bar the president from suspending congressional sanctions on Iran. The White House reluctantly went along with the legislation after some language was softened and once it became clear the measure would command veto-proof majorities.

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WINNING(equals)LOSING

Ironically, the resolution of disapproval ended up giving supporters of the deal the upper hand legislatively - in an upside-down sort of way.

The resolution is expected to come to a vote in the House and the Senate in the week ahead.

In the House, it is certain to pass. Republicans will vote for it unanimously and the Democratic minority is powerless to block it.

In the Senate, the outcome is uncertain. Sixty of 100 votes will be needed for the resolution to advance to a final vote. Republicans command 54 votes, and just three Democratic senators so far have announced their opposition to the accord. So Democratic and independent supporters may be able to muster the 41 votes needed to filibuster the resolution, or block a vote on final passage.

But even if the disapproval resolution does pass both chambers and makes it to Obama's desk, the president has promised a veto. It takes a two-thirds vote in the House and the Senate to override a presidential veto. That effectively makes it possible for just one-third of lawmakers in one chamber of Congress to green-light the deal by sustaining Obama's veto. The votes are already there to do that, in both chambers.

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SO?

When the House rejects the Iran nuclear deal this week, and even if the Senate does, too, Obama and his Democratic allies can rest easy knowing that the president will resort to a veto, the Democratic minority will back him up - and there's nothing Republicans can do about it, except fume.

Fume they have.

"The president may be able to sustain a veto with the tepid, restricted and partisan support of one-third of one House of Congress over Americans' bipartisan opposition," Senate Majority Leader Mitch McConnell, R-Ky., complained when Democrats locked up the 34 Senate votes this month to sustain Obama's veto.

At the same time, the upside-down situation has led to some conspiratorial suggestions on the left that Republicans are secretly happy they cannot block the deal, because this way they can avoid the uncertain outcome and potential international backlash were that to happen.

Opponents of the deal reject that suggestion. But some of them acknowledge feeling like they were set up to fail - that given the extremely high bar for overriding a presidential veto, they never had much of a chance.

"The way the administration chose to bring the agreement with Iran before Congress made it very hard for opponents of it to ever actually have the two-thirds votes necessary in both chambers to stop the agreement," said former Sen. Joe Lieberman of Connecticut, a Democratic-turned-independent who's a leader against the agreement.

"If this was considered a treaty, which I think it really was as important as any treaty," Lieberman noted, "the numbers would have been flipped."

So the tens of millions spent by the pro-Israel lobby, the overheated rhetoric from both sides, the very public agonizing by lawmakers for and against, and the fusillades lobbed by GOP presidential candidates - none of it had much of a chance of affecting the outcome.

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WHAT IF?

What if, somehow, congressional opponents were to prevail and the disapproval resolution went into effect? There is debate about the result, but some experts say that not even that could stop Obama from moving forward with the most significant elements of the nuclear deal on his own.

So for Congress, the political ramifications for lawmakers who angered constituents on one side or another with their decision on the deal may be profound and lasting.

But in a practical sense, the game is over and the Obama administration won, before this week's votes are even cast.

By AP