Democrats in the US Senate vowed to force Republicans to vote on a $1.8bn “MAGA slush fund” established as part of a resolution of Donald Trump’s long-shot lawsuit against the Internal Revenue Service.

The US president has described the secretive and loosely controlled “anti-weaponization fund” as a means of paying the victims of politicized prosecutions. Members of his own party are among those who have expressed alarm.

The terms of the fund do not require the disclosure of how much is paid to whom. Administration officials have said payees could include pardoned January 6 rioters.

“Trump’s nearly $2 billion MAGA slush fund is his most brazen act of self-dealing yet and one of the most corrupt schemes ever launched by a president,” Chuck Schumer, the US Senate minority leader, wrote in a letter to colleagues. “Senate Democrats will not let it stand.”

The president sued the federal government over the leak of his tax returns. The controversial fund was announced last month as part of a settlement in this lawsuit against the IRS, an agency the president controls through his appointees. The agency did not defend itself in the lawsuit, raising accusations of collusion and corruption. The legal and political backlash has been swift.

US district judge Leonie Brinkema in Virginia on Friday temporarily blocked the administration from transferring money from the fund after Democracy Forward filed a lawsuit to dissolve it.

Mike Pence, Trump’s first term vice-president, described the possibility of Capitol rioters who assaulted police officers and vandalized the US Capitol being compensated by the federal government as “deeply offensive” on Sunday. “And I think that’s broadly held by most Republicans and most Americans,” he told Meet the Press on NBC.

California’s governor, Gavin Newsom, has proposed a 100% income tax on any distribution of the fund to a California taxpayer. Similar proposals have emerged in Illinois, New York and Connecticut.

Schumer, describing the fund as “corruption in broad daylight”, said Democrats would force Senate Republicans to vote on a measure to block payments from the fund. Democrats will demand that records are preserved and will press for hearings, he said.

“If Republicans return to reconciliation, we will be ready with amendments to shut the fund down,” wrote Schumer. “If they try to bury the issue, we will force them to the Senate floor. If they try to sneak behind appropriations, we will fight them there too. There will be no escape hatch. No fake guardrails or backroom promises to hide behind. No Justice Department announcement that makes this corruption acceptable.”