Many people — myself included — thought that TPP would, in the end, follow the model of NAFTA: a Democratic president would push the agreement through Congress, but the bulk of the votes would be Republican. But it doesn’t seem to be going that way. Why?

Lydia DePillis suggests that procedural differences and the changed political environment are what changed. Maybe. But I’d suggest three additional factors.

First, while non-trade issues like dispute settlement and intellectual property already loomed large in NAFTA, it was nonetheless more of a genuine trade agreement than TPP — it was, or was perceived as by all sides, to an important degree about the integration of Mexican manufacturing into a North American industrial complex. This meant that conventional trade analysis seemed much more relevant than it does in the current dispute, where economists who try to lecture us about comparative advantage end up looking ridiculously out of touch.

Despite this, the real case for NAFTA involved foreign policy — which is also true for TPP (administration officials tell me that it’s really about geopolitics.) But that case was much more compelling for NAFTA, which was about rewarding Mexican reformers. In 1993, the risk that rejecting NAFTA would provoke an anti-US backlash and empower radicals seemed real and concrete. By contrast, geopolitical arguments for TPP are vague and nonspecific, involving prestige and influence and supposed Asian perceptions. Maybe so, but hard to sell (and why should we trust such claims?)

Finally, I think it’s fair to say that the liberal intelligentsia has been somewhat radicalized by Republican extremism; making common cause with those who share your basic values matters more than it seemed to a couple of decades ago. (And they wonder why the White House doesn’t see this.) Yes, I’m partly talking about myself, but it’s much broader than that; even Larry Summers is at best praising TPP with faint damns, so that most of his recent columns read more like a brief against the agreement than one in support.

So it really is a different game, and TPP supporters need to realize that old rules no longer apply.