One by one, Gary Gensler's supporters deserted him. Now the chief U.S. regulator of derivatives was being summoned by Treasury Secretary Jacob J. Lew to explain why he refused to compromise.

Banks and lawmakers, as well as financial regulators from around the world, had besieged Lew with complaints about Gensler's campaign to impose U.S. rules overseas.

The July 3 meeting in Lew's conference room with a view of the White House grew tense, according to three people briefed on it. Gensler argued his plan was vital if the U.S. hoped to seize meaningful authority over financial instruments that helped push the global economy to the brink in 2008, taking down American International Group Inc. (AIG) and Lehman Brothers Holdings Inc. and igniting the worst recession since the 1930s.