In a Washington Post column on the Trans-Pacific Partnership (TPP) Summers raises the right cautions. He argues that a trade deal should have rules that prevent countries from gaining a competitive advantage by deliberately lowering the value of their currency. He also argues that a deal should not be about special privileges for corporations. And, he says that a trade deal should not jeopardize public health by raising drug prices.

Nonetheless it looks like Summers is likely still going to come down for the TPP. His rationale is that a deal has large potential gains for the United States by making East Asian markets more open to the United States.

This is hard to see. Most of these markets are already largely open, so there will not be much gain from removing whatever barriers still exist to exporting to countries like Australia. Some of the other countries, most notably Vietnam, still have substantial barriers, but it's difficult to see large gains given their limited size.

In the case of Vietnam, our current exports are around $35 billion a year. Suppose this increases by 30 percent as a result of the TPP. (This would be a large increase; remember barriers to its imports from other countries are falling as well.) This would translate into a bit more than $10 billion a year in additional exports to Vietnam. If we assume that we get 20 percent more from selling these exports to Vietnam than they would otherwise fetch (a quite large premium) that would translate into $2 billion a year. That is equal to 0.01 percent of GDP.

Of course there will be gains from openings with other countries but the total is not likely to be very impressive. A study published by the Peterson Institute for International Economics put the gains from the TPP at $77 billion a year. This is equal to about 0.4 percent of GDP. That's not trivial, but not exactly a sea change in terms of American prosperity. (It's equal to about 2 months of normal growth.) And remember, the projection is that we don't see this full gain for a decade or more. Also, this says nothing about the distribution of the gains, which may go disproportionately to those at the top. (The model assumes full employment.)

Furthermore, this estimate took no account of measures that will almost surely slow growth, most notably higher drug prices due to stronger patent protections and higher prices for other goods due to stronger copyright protection. These increased protections have the same impact as imposing large excise taxes on the items covered. (The impact of patents on drug prices is comparable to taxes in the range of 1,000-10,000 percent.)

There is an argument that these measures will provide more incentive to innovate and do creative work, but don't hold your breath on that one. When we retroactively increased the length of copyright protection from 75 to 95 years, did we give a lot of incentive to people in 1920 to do more creative work?

Anyhow, it is likely that the actual deal will have bad provisions on drugs, will include large corporate giveaways on the regulatory front, and have nothing on currency. For this reason, the TPP looks like lots of downside with not much upside.