Mr. Wyden said he was also examining the approach. The rescinded alternative minimum tax was once intended to make sure the rich paid some significant amount and kicked in as a parallel system once taxpayers claimed a certain number of deductions.
But Mr. Wyden said it was devised to target high income, not high wealth, and ended up letting the richest of the rich skate free. He said he would act to close the so-called carried-interest loophole, which allows many hedge fund and private equity managers to declare income fees as capital gains from their clients and pay a far lower rate on them.
“We need to be more aggressive,” said Senator Sherrod Brown, Democrat of Ohio and a member of the Finance Committee. “The whole Republican message has been: ‘Pay less taxes, have more economic growth.’” He added, “They’ve had their way for too long, and we haven’t had enough Democrats that have wanted to stand up to it.”
Most Republicans are not changing their positions. Senator Charles E. Grassley of Iowa, a senior Republican on the Finance Committee who once aggressively went after tax avoidance, said he was most outraged not by the content of the ProPublica report but by the fact that so much private tax data had leaked.
His concern was that any effort to tax the value of assets before their sale would hit farms and privately held businesses. Taxing the capital gains of the superrich as income, he said, “would retard investment, which creates jobs.”
Mr. Toomey, another committee member, was more open, though he said he wanted to make sure the ProPublica report was accurate and that he understood the mechanics of the tax avoidance before latching onto a blunt instrument like a new alternative minimum tax.
“I’d rather try to understand if it’s true, what the dynamic is that makes it true and to do something about it,” he said.