Charles Rangel, the powerful New York Democrat congressman, was instrumental in protecting a tax loophole that benefitted an oil-drilling company run by a benefactor of his pet project: the Charles B. Rangel School of Public Service at C.C.N.Y., for which he has raised a total of $11 million.

Nabors Industries, was one of four corporations based in the United States that were widely criticized in 2002 and 2003 for opening offices in the Caribbean to reduce their federal tax payments. Mr. Rangel was among dozens of representatives from both parties who bitterly opposed those offshore moves and, in 2004, pushed unsuccessfully for legislation to make the companies pay more tax.

But in 2007, when the United States Senate tried to crack down on the companies, Mr. Rangel, who had recently been sworn in as House Ways and Means chairman, fought to protect them. The tax shelter for the four companies was preserved, saving Nabors an estimated tens of millions of dollars annually and depriving the federal treasury of $1.1 billion in revenues over a decade, according to a Congressional analysis by the nonpartisan Joint Committee on Taxation. ...

Mr. Rangel also said that the pledge from the Nabors chief executive, Eugene M. Isenberg, one of the largest the school received, played no role in his decision to protect the loophole.