Following months of delays that critics said may have weakened their legal hand, House Democrats on Tuesday sued the Internal Revenue Service and the Treasury Department over their refusal to release President Donald Trump's personal and business tax returns.

"Trump has been gifted several months of delay in litigation that can never be recovered by the public that voted Democrats into control of the House of Representatives as a check on Trump's corruption."

—Jeff Hauser, Revolving Door Project

In the 49-page lawsuit, Rep. Richard Neal (D-Mass.), chairman of the House Ways and Means Committee, accused Treasury Secretary Steve Mnuchin and IRS Commissioner Charles Rettig of mounting "an extraordinary attack on the authority of Congress" by blocking the release of the president's tax documents.

Jeff Hauser, director of the Revolving Door Project at the Center for Economic and Policy Research, said Tuesday that while the lawsuit (pdf) is "generally very well done," Neal's decision to wait months before filing it was "a win for Trump, regardless of the eventual outcome in court."

"Today, we are 90 days since Neal asked nicely for Trump's tax returns," Hauser said in a statement. "It has been 83 days since Mnuchin 'missed the deadline' to hand them over, 80 days since Neal asked nicely again, and 70 days since Mnuchin 'missed' Neal's extended deadline. It has been 57 days since Mnuchin issued his 'final' denial of Neal's request, 53 days since Neal issued a subpoena for the tax returns, and 46 days since Mnuchin rejected the subpoena."

"Trump has been gifted several months of delay in litigation that can never be recovered," Hauser added. "That delay did nothing to strengthen the House's already strong legal hand, but can and will be used by Trump as evidence that there is no constitutional urgency here that would warrant a court expediting this case."

Quoted in @business on Neal's long-delayed lawsuit: https://t.co/XO4D7gRa7J I will add -- the lawsuit is generally very well done, even as I believe it should include an explicit reference to https://t.co/0eICmPVDwN (it makes this point implicitly) pic.twitter.com/tA9ztEnSQy — Jeff Hauser (@jeffhauser) July 2, 2019

Neal has been facing grassroots pressure to sue the Trump administration since May, when Mnuchin refused to comply with a subpoena for the president's tax documents.

Progressive advocacy groups that criticized Neal for slow-walking the process of obtaining Trump's tax returns applauded the belated lawsuit as a crucial step in the face of White House stonewalling.

"We commend Chairman Neal for taking this necessary action to finally get answers on behalf of the American people about what Donald Trump is hiding—and who he may be beholden to," Ryan Thomas, spokesperson for Stand Up America, said in a statement. "No one is above the law. And Congress must not allow administration officials like Mnuchin—and certainly not Trump himself—to think they are."

#BREAKING: House Democrats have filed a lawsuit to force the Treasury Department to turn over Trump's tax returns, after @StevenMnuchin1 refused to comply with a lawful subpoena. Finally.https://t.co/WatZNnSkPU — Stand Up America (@StandUpAmerica) July 2, 2019

As the Washington Post reported in May, an internal IRS memo said the Treasury Secretary is legally obligated to hand over the president's tax returns, despite Mnuchin's claim that House Democrats' request is an abuse of power.

Legal experts have expressed the same view, arguing the law clearly states that Mnuchin must release the tax documents upon request from Congress.

"The statute is very clear and seems like very strong support for what Mr. Neal is trying to do," George K. Yin, a professor at the University of Virginia School of Law and former chief of staff of the Joint Committee on Taxation, told Roll Call in April. "I think [Mnuchin] obviously needs to think very seriously about that; now he might not care if he gets fired, but I think he would care if he gets sent to jail."

In a statement on Tuesday, Frank Clemente, executive director of Americans for Tax Fairness, said it is "unfortunate that the committee has to resort to court action to compel the president to do what every past president for 40 years has done voluntarily."

"The public deserves to know if the president is a serial tax dodger (as we suspect), has compromising financial relationships with public officials or business people in Russia or other foreign countries, or has any other conflicts of interest that could adversely affect the exercise of his official duties, such as legislation he wants Congress to enact into law," Clemente said.