I think I know who you're talking about.
The original agreement happened at a time when about 80% of the vehicles made in North America were made in the Great Lakes region. There was the idea that for Great Lakes states, if we opened the door to Mexico or Canada, there was going to be some erosion. That's why he voted against it.
This time, the agreement raises the regional value content but also turns around specifically on vehicle parts, on a section called core parts, and says—and these are the six most added-value parts, the ones you think they are: engines, transmissions, suspensions—if you're going to use steel to make those parts, or you're going to use aluminum to make those parts, 70% of that has to be sourced regionally.
Simply put, if he is representing a district that's in the automotive-manufacturing sector or in steel, this agreement favours those regions. Specifically with the provision for labour value content, if you make a car in a facility that pays less than $16 an hour—that's the wage, not the fully-loaded cost of labour—then 40% of that car has to come from parts facilities that pay $16 an hour. Presumably, if they're making those core parts, they're making them with 70% local steel.
It's a really simple binary decision for anybody who is in a manufacturing district or riding. For automotive steel and aluminum, this agreement guarantees more content than the one it replaces. For any of the three signatory countries, it is the first one in 25 years that raises that number.