Taking head-on a lot of myths about trade promotion authority, CRS explains how TPA puts Congress in the driver’s seat of trade negotiations.

"Even though the TPA procedures are designed to ensure that Congress will act on implementing bills, and will do so without amending them, TPA legislation affords Congress several procedural means to maintain arguably tight reins on the executive branch's exercise of the delegated trade authority," the report says. Specifically, "TPA statutes include extensive, specific negotiating objectives to be pursued in covered trade agreements." They also "include extensive requirements for Congress to be notified of any trade agreement negotiations and consulted during their course."

The report emphasizes that TPA will allow Congress to be proactive, instead of reactive to whatever trade agreements the President puts in front of it:

In as much as an implementing bill (if considered under the statutory expedited procedure) normally cannot be amended, however, the revenue committees [that is, the House Ways and Means Committee and the Senate Finance Committee] exercise control in these cases instead through actions to shape the content of the implementing bill before it is introduced.

And can TPA—or any agreement negotiated under it—change U.S. law without Congress’s sign-off? Not a chance:

The proposed TPA-2015 states that no provision of any trade agreement entered into under the TPA in consistent with any law of the United States, of any State, or any locality of the United States could have any effect. Nor could any provision of a trade agreement prevent the government of the United States, of any State, or any U.S. locality from amending its laws.