A group of former Republican lawmakers are supporting Manhattan District Attorney Cyrus Vance Jr. in a case before the Supreme Court over New York prosecutors' grand-jury subpoena for President Trump Donald John TrumpBarr criticizes DOJ in speech declaring all agency power 'is invested in the attorney general' Military leaders asked about using heat ray on protesters outside White House: report Powell warns failure to reach COVID-19 deal could 'scar and damage' economy MORE's tax returns.

In a brief filed Monday, the former Republican lawmakers — along with prominent Trump critics such as John Dean and George Conway George Thomas ConwayGeorge Conway hits Trump on 9/11 anniversary: 'The greatest threat to the safety and security of Americans' Susan Collins faces battle of lifetime in Maine Conway hails Trump as 'champion' of women MORE — pushed back on the argument made by Trump's lawyers that presidents have sweeping immunity from the criminal process.

They said in their brief that they are "concerned that President Trump’s assertions of absolute immunity from process while in office—and more generally, his arguments against accountability in any forum—could impose lasting damage on our constitutional system of checks and balances as well as on the rule of law."

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The brief comes before the Supreme Court is set to hear oral arguments in the case on March 31.

The Manhattan district attorney's office in August issued a grand-jury subpoena to Trump's accounting firm, Mazars USA, for the president's tax returns and other financial records. The DA's office is seeking the documents as part of an investigation into payments made to two women with whom Trump allegedly had affairs.

Shortly after the subpoena was issued, Trump's personal lawyers sued to block it, arguing that the subpoena is unconstitutional because presidents can't be criminally investigated while in office. Federal judges at the district and appeals court levels ruled against Trump. The case is now pending before the Supreme Court.

The former GOP lawmakers said in their brief that the Constitution doesn't bar subpoenaing the president for documents related to unofficial actions.

"The Framers designed a system in which no one is above the law, not even the president," the former lawmakers wrote. "Historically, this Court has adhered to that principle. It should do so again and affirm the decision of the Second Circuit."

The signers of the brief include a number of former GOP lawmakers who served in Congress in the 1980s and 1990s, as well as a few former lawmakers who left Congress more recently, such as former Wisconsin GOP Reps. Thomas Petri and Reid Ribble Reid James RibbleFormer Sen. Tom Coburn dies at 72 Ex-GOP lawmakers side with NY in Supreme Court case over Trump tax returns Former GOP lawmakers, officials ask court to enforce House subpoena on McGahn MORE. Others who signed the brief include former officials in Republican administrations, such as Christine Todd Whitman, who led the Environmental Protection Agency at the beginning of George W. Bush's presidency.

The Supreme Court is also scheduled to hear oral arguments on March 31 in two cases where House Democrats are seeking Trump's financial records from Mazars, Capital One and Deutsche Bank.