A Washington, D.C.-based federal judge has sided with House Oversight Committee Democrats seeking to enforce their subpoena of Trump accounting firm Mazars USA, in a major ruling that breathes new life into Democrats' ongoing efforts to probe the president's financial dealings.

The subpoena seeks access to a slew of Trump financial documents dating back to 2011, including personal records and records of various affiliated business and entities. Democrats pursued the subpoena after former Trump lawyer Michael Cohen testified to Congress in February that the president's accountants routinely and improperly altered his financial statements -- including some signed by Mazars -- to misrepresent his assets and liabilities.

Barack Obama-appointed judge Amit P. Mehta's 41-page opinion began by comparing President Trump's concerns about congressional overreach to those of President James Buchanan, asserting that Trump "has taken up the fight of his predecessor."

And Mehta acknowledged a high likelihood that any documents obtained by House Democrats would quickly leak, and become partisan political fodder.

"[T]he court is not naïve to reality," Mehta wrote, admitting there "is a chance that some records obtained from Mazars will become public soon after they are produced."

Mehta added that he was "well aware that this case involves records concerning the private and business affairs of the President of the United States," dating back to well before he declared his candidacy.

But, Mehta said, Democrats' subpoena fell within established congressional investigative and oversight powers, which generally only require that subpoenas serve some "valid legislative purpose." The judge noted that the probe could uncover conflicts of interest in the White House, as well as potential violations of the Foreign Emoluments Clause or the reporting requirements of The Ethics in Government Act of 1978.

Mehta said he would not stay his ruling pending appeal, despite the risk of permanently compromising Trump's private financial information, in part because of the public's strong interest in Democrats obtaining the records. That means the subpoena will take effect within 7 days unless it is stayed by another court on appeal.

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"Courts have grappled for more than a century with the question of the scope of Congress’s investigative power," Mehta wrote. "The binding principle that emerges from these judicial decisions is that courts must presume Congress is acting in furtherance of its constitutional responsibility to legislate and must defer to congressional judgments about what Congress needs to carry out that purpose. To be sure, there are limits on Congress’s investigative authority. But those limits do not substantially constrain Congress."

The judge continued: “It is simply not fathomable that a Constitution that grants Congress the power to remove a President for reasons including criminal behavior would deny Congress the power to investigate him for unlawful conduct—past or present—even without formally opening an impeachment inquiry."

The president’s legal team, in a filing earlier this month, had asked the judge to prohibit Mazars from “enforcing or complying” with the subpoena, issued April 15.

Trump's lawyers quoted Democrats as openly admitting they wanted to use subpoena power for political purposes. “We’re going to have to build an air traffic control tower to keep track of all the subpoenas flying from here to the White House," one Democrat said; another referenced a "subpoena cannon" firing at the White House.

Trump's lawyers also argued the subpoena to Mazars “lacks a legitimate legislative purpose,” and is an “unconstitutional attempt to exercise ‘the powers of law enforcement.’”

But, Mehta wrote in his ruling, the standard for obtaining a valid congressional subpoena is not a difficult bar to clear under Supreme Court precedent, and Democrats had easily shown they were not simply out on a "fishing expedition." Comments made by Democrats suggesting their political motivations, Mehta said, did not automatically make the subpoena itself invalid.

"The Oversight Committee has shown that it is not engaged in a pure fishing expedition for the President’s financial records," the judge wrote. "It is undisputed that the President did not initially identify as liabilities on his public disclosure forms the payments that Michael Cohen made to alleged mistresses during the presidential campaign. Furthermore, Michael Cohen has pleaded guilty to campaign finance violations arising from those payments."

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Trump’s lawyers also noted that the House Oversight Committee, led by Chairman Elijah Cummings, D-Md., is leading several Trump-focused investigations.

"The Oversight Committee has shown that it is not engaged in a pure fishing expedition for the President’s financial records." — Washington, D.C. district court Judge Amit P. Mehta

“Chairman Cummings flat-out admitted that he wanted to ‘investigate whether the President may have engaged in illegal conduct before and during his tenure in office’ and ‘review whether he has accurately reported his finances to the Office of Government Ethics and other federal entities,’” Trump’s lawyers wrote in the filing.

Meanwhile, House Oversight Commitee ranking member Jim Jordan, R-Ohio, called the subpoena “an unprecedented abuse of the Committee’s subpoena authority to target and expose the private financial information of the President of the United States.”

The Trump team filing came after Cummings’ committee issued several subpoenas for Mazars Accounting in an effort to obtain financial documents and audits prepared for Trump and his businesses over the last decade.

Cummings also sought independent auditor’s reports, annual statements and other documents related to Trump’s finances spanning from 2011 to 2018.

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At the time, Mazars said it “will respect the legal process and fully comply with its legal obligations.”

The ruling comes the same day that Trump directed former White House Counsel Don McGahn to skip a House Judiciary Committee hearing scheduled for Tuesday, citing a Justice Department opinion that he cannot be compelled to testify about his official duties.

In a statement released Monday afternoon, White House Press Secretary Sarah Sanders blasted Democrats for continuing to pursue Trump investigations, saying they want a "wasteful and unnecessary do-over" in the wake of Special Counsel Robert Mueller's probe -- and describing the subpoena for McGahn as part of that effort.

Mueller's investigation, with resources and legal authority far exceeding that of Congress, resulted in the prosecutions of several former members of Trump's orbit for financial crimes. But in addition to failing to find any evidence of improper collusion with Russia, Mueller returned no evidence of financial misconduct by the president.

Fox News' Bill Mears, Edward Lawrence, Brooke Singman, and Kristin Brown contributed to this report