There's only one thing economists love more than free trade. That's telling everyone else why they should love free trade too.
Trade is already mostly free between the U.S. and Europe -- as Deardorff said, "it's the same stuff going across the Atlantic with different brand names" -- with tariffs averaging just 3 to 4 percent. Now, as Deardorff explained to me, the efficiency losses from trade barriers rise with the square of the tariff -- so once tariffs get low, the harm they're doing gets lower. In other words, Deardorff couldn't "really see it would be a big deal" to move from 3 to, say, 1 percent tariffs with Europe. But even that probably overstates how much would get negotiated. Thorny issues like anti-dumping rules, regulations, and agriculture subsidies probably wouldn't be part of any deal, especially the latter since that would allow other countries to demand equal treatment. Indeed, the German-based Ifo Institute estimates a smaller deal focusing on reducing custom duties would only increase GDP per capita by about 0.1 to 0.2 percent.