With high-stakes Senate votes set this week on whether to grant President Obama “Fast Track” authority to negotiate the Trans-Pacific Partnership trade deal, the prospects for success turn on the big question of whether a bloc of 14 pro-TPP Senate Dems will swallow hard and vote Yes.

There’s basically one factor that will determine how those pro-TPP Dems vote: whether they think Congress will pass Trade Adjustment Assistance for workers after they pass Fast Track. That will turn on whether Mitch McConnell and John Boehner make good on their vow to pass TAA — but it will also turn on whether enough House Democrats and liberals end up supporting TAA to get it through the lower chamber at the end of the day.

It’s looking increasingly like those House Dems and liberals — who had previously opposed TAA as a way to kill Fast Track — may have been backed into a corner and may have no choice but to support TAA in the end. And, thanks to the convoluted process that has evolved within Congress on trade, that seeming reality as to what will happen later may be what enables pro-TPP Senate Dems to pass Fast Track first, reviving Obama’s trade agenda.

The White House is set to ramp up its case to House liberals and Dems that they should support TAA later, after Fast Track passes, arguing that a broad Senate package has been crafted around TAA that is loaded with things they should want. If the Senate passes Fast Track, next up in the Senate will be a package that doesn’t just include TAA, but also includes the African Growth and Opportunity Act, which is designed to boost trade with sub-Saharan countries, a system of trade preferences for poor nations, and a provision to help the domestic steel industry that is sought by Senator Sherrod Brown.

The Senate GOP leadership is set to hold those two votes this week. All eyes are on the bloc of 14 Dems who helped pass Fast Track out of the Senate last time, when it was packaged with TAA. The question is, if Fast Track alone does pass, how do House Democrats oppose that second round of proposals?

Remember, House Democrats support TAA, and had only previously voted it down in the House as a back-door way of killing Fast Track, because the two were packaged together. That worked — temporarily. But now the whole equation may be set to change.

After House Dems sank the Fast Track/TAA package, House GOP leaders held a vote only on Fast Track, which succeeded. If pro-TPP Senate Dems — who had previously supported Fast Track only as part of a package including TAA — now help pass Fast Track out of the Senate by itself, sending it to the president, House Democrats will no longer have any reason to oppose the TAA package. After all, they’d only opposed it to bring down Fast Track. If Fast Track is sitting on the president’s desk, awaiting his signature, then the question for House Dems becomes whether Fast Track — and the TPP — move forward with or without the TAA package. That puts them in a very tough position.

Several House Democratic aides conceded to me that if the Senate passes Fast Track, then it will be hard for House Dems to oppose the TAA package. Around 80 or more House Republicans are expected to support TAA — which means you’d need at least 140 House Dems to pass it. But how many will vote No on worker assistance at the end of the day, in a situation where Fast Track is set to become a reality no matter what they do?

This is an extremely odd situation. House Dems cannot telegraph that they will vote for the TAA package later if Fast Track is sitting on the president’s desk, because then that makes it easier for the pro-TPP Senate Dems to pass Fast Track first. Politico reports that only one of the pro-TPP Dems is a hard No on Fast Track — Maria Cantwell — though there’s still plenty of uncertainty remaining. The White House can only afford to lose three of them.

It’s certainly possible that enough Senate Dems will balk and vote No on Fast Track if House Dems can keep alive fears of the possibility that TAA might fail later. But those Senate Dems may roll the dice and vote Yes. At that point House Dems might have to vote for the TAA package. Of course, in the end, even if they failed to block Fast Track, by getting Senate negotiators to load up that TAA package with other stuff they want, House Dems might have succeeded in making it significantly better than it otherwise might have been.


UPDATE: Senator Ron Wyden, a key member of the bloc of 14 pro-TPP Dems, just announced he will vote Yes on the Fast Track bill, making it more likely that it passes — and more likely that House Dems and liberals will indeed face the dilemma outlined above.