But another, less discussed, piece of the puzzle is the rules of origin. These rules dictate what percentage of a good's components need to be manufactured in TPP member countries for those products to qualify for duty-free status. As a 2013 Heritage Foundation brief recognized, these rules "can make or break the Trans-Pacific Partnership."
American manufacturers (and certainly workers) generally want higher percentage rules so that component competitors in nonpact countries can't benefit from decreased tariffs. On the other hand, too stringent rules risk distributing the deal's benefits to few — or none — as nearly every company uses an increasingly global supply chain.
While the North American Free Trade Agreement requires an auto to include 62.5 percent of its content value in order to qualify for the deal, TPP will only need 45 percent.
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"If you're a U.S. steel manufacturer, for example ... there's a scenario now where China can supply the steel or make more than half the input, and if the rest is done in Malaysia or Vietnam, it's now a product of TPP and eligible for duty-free treatment," Brightbill said. "It's hard for me to see how that will help U.S. manufacturing in general."
Another rules of origin problem for U.S. firms may be their complexity, as the TPP "risks rendering firms uncertain how to take advantage of treaty terms and confusing customs agents charged with administering those terms," according to Scissors.
Other parts of the TPP deal are less easy to grade before their implementation. Experts have alternately praised and criticized the rules governing state-owned enterprises. The first-of-their-kind agreements make key headway in an important issue facing American companies, but some, including Scissors, worry that they don't go far enough, and therefore establish a loose precedent.
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All in all, Brightbill said many of his corporate clients are concerned about how the TPP would shake out if approved.
"They are great companies that are world-class competitive, and yet they struggle to export around the world because of trade barriers in many other countries, including TPP countries," he said. "For them, if they can get their products into these markets it would be a big win, but they are very concerned that we are simply opening our market ... and we won't see real market opening from countries like Korea, Japan, Malaysia and Vietnam."
In fact, he said, while the U.S. remains a relatively easy market to enter, some countries have barriers —regulatory and otherwise — that trade agreements have difficulty addressing.