As a staffer on Capitol Hill when Barack Obama was elected, I was in the meetings with AIPAC in which -- facing a president with enormous political capital and a pro-diplomacy agenda -- they claimed to support talks with Iran. This despite the savaging that Obama as a candidate endured from Iran hawks and so-called "pro-Israel" groups because of his pledge to break with the Bush administrations refusal to engage adversaries.

But in those Hill meetings, we weren't being lobbied to support diplomacy, we were being lobbied to sign onto sanctions that AIPAC said were necessary as the next step if and when the talks did not yield results. Those sanctions would become a self-fulfilling prophecy.

We now know what would happen next -- Netanyahu pressed Obama to place artificial timetables on engagement, and Congress wielded the threat of passing unilateral crippling sanctions like a sword of Damocles over the U.S.-Iran talks.

Sure enough, after much back and forth, once Iran eventually accepted a deal to ship out its low enriched uranium (after Netanyahu's imposed deadline had expired), it was too late -- Congressional sanctions were already queued up for quick passage. The president could choose to pursue Iran's offer and watch Congress upend it by passing unilateral sanctions, also scuttling a hard fought multilateral sanctions resolution queued up at the UN. Or, he could reject Iran's offer and implement the UN sanctions in the nick of time before Congress passed their unilateral sanctions. Either way, Congress was going to pass its sanctions.

The president went with option B, and now we have some of the most stringent multilateral and unilateral sanctions ever in place on a country, but no progress in terms of actually resolving the Iranian nuclear standoff.

While this was all happening, the refrain from Congress (and AIPAC) was that we couldn't let Iran buy time; so long as the negotiations were happening, they said, Iran's centrifuges were spinning. The irony is that over the past three years, as we've sanctioned instead of negotiated, Iran's centrifuges still continue to spin.

This time around, Congress is again waving sanctions as the sword of Damocles over new talks -- warning that Iran is just "buying time," and threatening sanctions that will sabotage any potential progress.

What is on the line at the talks is capping Iran's nuclear program -- preventing Iran's centrifuges from enriching uranium closer to the weapons grade that is the real concern, and paving the path for a continued diplomatic process that is the only way to impose inspections and transparency that can prevent a nuclear armed Iran.

Furthermore, such measures that steer us in the direction of a diplomatic endgame, rather than war, can tamp down gas prices and immediately benefit ordinary Americans -- who are paying an estimated five dollar "loose war talk" surtax every time they fill up their gas tanks.

To achieve near-term concessions on the Iranian side, and to build on those measures, sanctions will likely need to be leveraged -- whether by freezing them at current levels or easing some of them. But instead of providing the president with the flexibility to utilize the sanctions for their intended purpose -- as leverage -- expect a major Congressional push in the opposite direction, to instead expand sanctions and ensure the president can't use them for diplomatic progress.

Additionally, there will likely be a redoubled Congressional effort to press forward with a stalled AIPAC and Netanyahu-endorsed push to redefine the diplomatic endgame in such a way as to rule out any plausible, inspections-based solution. This is effectively an effort to shift the goal posts and demand a maximalist, unachievable endgame, including that Iran end all enrichment and ship out all nuclear material.

The main vehicle for this push is the "red lines" resolution (S.Res.380/H.Res.568), which states that the U.S. cannot contain a nuclear weapons capable Iran, rather than the president's defined red line of a nuclear weapons armed Iran. Ruling out "capability," though the term has not been defined, could bar any solution in which Iran maintains even a highly monitored enrichment program -- the only plausible solution to the Iranian nuclear standoff.

So, if the talks this weekend yield progress, hawks will say, "Ah ha -- that progress was only because of sanctions, so we need more and we need to shift the goal posts to achieve maximalist ends." If the talks don't yield progress, hawks will say, "Ah ha -- that stalemate is because the sanctions are not crippling enough, so we need more and we need to shift the goal posts to ensure maximalist ends." Either way, Congress is pushing its sanctions. And if a new Congressional sanctions push is successful, the president may be blocked -- either politically or perhaps even legally -- from leveraging sanctions in exchange for Iranian concessions, killing any deal.