When Eric Cantor delivered his farewell address on the House floor this summer following his stunning primary defeat, the former majority leader cited the enactment of the Gabriella Miller Kids First Research Act as "one of my proudest moments."

This was not a landmark piece of legislation, but it redirected federal dollars from the public funding of political conventions to pediatric research. It was a feel-good, impossible-to-oppose measure that won nearly 300 votes in the House and was passed by unanimous consent by the Senate. After all, who could argue that the quadrennial party conventions—glitzy coronations that long ago morphed into political infomercials—needed public funding in an electoral system awash with outside money? Didn't the two major parties get enough from private donors?

It turns out the answer to the second question was no. With a last-minute provision tacked onto page 1,599 of the 1,603-page, $1.013 trillion spending bill, Congress is moving to fill the void left by the stripping of public funds for the party conventions by dramatically increasing the amount that individual donors can contribute to the various Republican and Democratic committees.

Speaker John Boehner on Wednesday explained the change by pointing to the Kids First Research Act. "This provision was worked out in a bipartisan way to allow those who are organizing political conventions to raise the money from private sources as opposed to using taxpayer funds," he told reporters. Yet according to advocates for campaign-finance reform, the change will affect a lot more than the financing of political conventions. A single (presumably ultra-wealthy) donor who can currently give a maximum of $97,200 to national party committees would be able to contribute nearly eight times as much—a total of $776,000 a year—to those organizations.

Reform advocates were apoplectic when they saw the language, to say the least. “If enacted, these changes will be the most destructive and corrupting campaign-finance provisions ever enacted by Congress," Fred Wertheimer, president of Democracy 21, said in a phone interview Wednesday. The director of Public Citizen's Congress Watch division, Lisa Gilbert, said that the extent of the change "far exceeds the fears that we had."

"It opens the floodgates to even more special-interest money coming into the party committees," Representative Chris Van Hollen, a senior House Democrat, said in an interview Wednesday after announcing his opposition to the spending bill. He noted that the changes do not just allow bigger donations for conventions, but for the construction of buildings and legals fees for electoral recounts as well.

Republican officials, including a former top aide to Cantor, said the change to campaign-finance laws had not been a major part of the discussions surrounding the pediatric research measure, which President Obama signed in April. "Our focus was on the bill itself and having more funds directed to pediatric research," the former Cantor adviser said. Reform advocates had opposed the bill because of fears that it would contribute to the dismantling of the public financing system, but the need to offset the loss of taxpayer funding with higher private limits "was definitely never explicitly said," Gilbert recalled. She said attributing the change as a follow-up to the Kids First Research Act was "a cover" for politicians who have been trying to loosen campaign-finance regulations since before a series of favorable Supreme Court decisions struck down important contribution limits.

Wertheimer said the extent of the changes took the reform community completely by surprise. "No one knew about this," he said. Of Boehner's argument that it was necessitated by the research measure earlier this year, he fired back: "That is the equivalent of the individual who kills his parents and then pleads for mercy as an orphan."

Beyond the sneaky inclusion of the change in the back of an unrelated, $1 trillion spending bill, the move highlights the new power of Mitch McConnell, the incoming Senate majority leader who has become one of the loudest champions of unrestricted political donations as a First Amendment cause. It was McConnell and Boehner, a Republican congressional aide said, who ensured that the campaign provision would be added to the omnibus in recent days. Progressive Democrats have long pushed for an expansion of public financing of elections, a movement that is now dead for the foreseeable future.

Democrats on Wednesday afternoon were scrambling to cut that provision out of the bill, along with another change rolling back a derivatives regulation in the Dodd-Frank Wall Street reform law of 2010. “These provisions are destructive to middle class families and to the practice of our democracy. We must get them out of the omnibus package," House Minority Leader Nancy Pelosi said in a statement.

Already concerned about losing support from conservatives, Republican leaders need some Democratic votes to ensure passage of the bill by a Thursday midnight deadline for averting a government shutdown. With mounting opposition from liberals, that outcome could be in doubt. "It's just too hard to tell at this point," Van Hollen said.