WASHINGTON  The White House has worked aggressively to shift attention from the plan to continue the Bush-era tax cuts for high-income taxpayers and to focus instead on how its deal with Republicans will stimulate the economy. But many Congressional Democrats say one component in the package will stimulate nothing except their continuing fury: a generous tax exemption for wealthy estates that will benefit only a small number of super-rich Americans.

“These guys were outmaneuvered in the negotiation at the price of $25 billion on the national credit card, made payable to 6,600 families,” said Representative Chris Van Hollen, Democrat of Maryland, who represented House Democrats in the formal negotiations on the tax issue, even as the White House was cutting a deal in secret talks with Republican leaders. “The estate tax is the choking point for the great majority of our members,” Mr. Van Hollen said.

The Senate on Thursday opened its first full day of debate on the $858 billion tax package, and the one person who seemed to have a lot to say about it was its fiercest opponent: Senator Bernard Sanders, independent of Vermont. He spent more than eight hours on the floor railing against the plan to continue the tax policies of George W. Bush, as well as the estate tax proposal, which is more generous to wealthy estates than in any year of Mr. Bush’s presidency.

“This nation has a record-breaking $13.8 trillion national debt at the same time as the middle class is collapsing and poverty is increasing,” Mr. Sanders said. “It seems to me to be unconscionable, unconscionable for my conservative friends and for everybody else in this country to be driving up this already too high national debt by giving tax breaks to millionaires and billionaires who don’t need it.”