A federal appeals court on Friday rejected President Donald Trump's attempt to block a House Oversight Committee subpoena demanding eight years of his financial records.

"We're one step closer to holding him accountable today," tweeted progressive advocacy group Tax March in response to the ruling by the U.S. Court of Appeals for the D.C. Circuit.

The decision in the case was 2-1, with Trump appointee Neomi Rao dissenting. The ruling affirms a lower court decision that ordered Mazars USA, Trump's longtime accounting firm, to turn over eight years of the president's tax and financial documents.

"Today's ruling is a fundamental and resounding victory for congressional oversight, our constitutional system of checks and balances, and the rule of law," Rep. Elijah Cummings (D-Md.), chairman of the House Oversight Committee, said in a statement. "For far too long, the president has placed his personal interests over the interests of the American people. After months of delay, it is time for the President to stop blocking Mazars from complying with the committee's lawful subpoena."

Eric Colombus, who served in the Justice Department under President Barack Obama, warned Rao's lonely dissent means "Dems shouldn't pop corks just yet."

"The Trump appointee dissented," Colombus tweeted, "giving Trump some hope that he might eke out a (ridiculous) win" if he appeals the ruling to the Supreme Court.

The court's 66-page majority opinion, authored by Judges David Tatel Patricia Millett, rejects Trump's argument that House Democrats' subpoena lacks legislative purpose and stresses that Congress has the constitutional authority to conduct oversight of the president.

"Contrary to the president's arguments, the committee possesses authority under both House rules and the constitution to issue the subpoena, and Mazars must comply," the opinion states.

Tatel and Millett cite former Supreme Court Justice Louis Brandeis's 1926 argument that the purpose of separation of powers is "not to avoid friction, but, by means of the inevitable friction incident to the distribution of the governmental powers among three departments, to save the people from autocracy."