WASHINGTON — The chairman of the Federal Reserve opposes it. The country’s chief banking regulator dislikes it. The secretary of the Treasury has been unsupportive, at best, and Paul A. Volcker — no one’s idea of a best friend to Wall Street — calls it unnecessary.

Their antipathy is directed at a proposal from Senator Blanche Lincoln, Democrat of Arkansas. She wants banks to get rid of their lucrative derivatives operations because they played an outsize role in the financial debacle. And when Wall Street needed a rescue, Mrs. Lincoln says, taxpayers should not have had to bail out bankers’ bad bets.

But just how far Democrats will pull back from an outright prohibition is unclear. Mrs. Lincoln is in a vicious primary campaign. Her opponent has tried to portray her as a Washington insider cozy with Wall Street and big business. If Mrs. Lincoln is seen as having given ground to bankers on derivatives, she could lose her job — and Democrats might well lose the seat to a Republican this fall.

In the month since Mrs. Lincoln offered her proposal, Democrats have played a waiting game. But in that time, opposition has grown and bank lobbyists have fought her plan, what they call the “push out” provision. The question now is whether after the Arkansas vote, on Tuesday, Democrats will argue that other safeguards in Mrs. Lincoln’s derivatives bill — requiring them to be traded on an exchange, processed through a third party and backed by sufficient collateral — will be sufficient.