Anthony P. Polito (Suffolk) has published Trade or Business in the United States: What Domestic Activity Suffices to Conduct a Foreign Trade or Business "in" the United States?, 36 Tax Mgmt. Int’l J. 496 (2007).  Here is the abstract:

Whether a particular set of activities constitute the conduct of a trade or business within the United States is a pressing question for many foreign taxpayers. The answer determines what form of U.S. taxation, if any, applies to many foreign taxpayers. The article examines the body of case of law and IRS rulings and concludes that, in the international context, this question needs to be bifurcated into two distinct inquiries:

• Is the foreign taxpayer engaged in a trade or business?
• Is the conduct of the trade or business in the United States?

The answer to the former question is quantitative. Are the taxpayer’s activities sufficiently regular, continuous, and considerable to constitute a trade or business? Once the existence of a trade or business is established, however, no minimum quantum of U.S. activity is necessary to bring a foreign trade or business into the United States. The answer to the second question is qualitative. In addition to the analysis producing this conclusion, the article illustrates its application in a number of specific fields of economic activity.