* Justices to hear three financial records cases on May 12
* Rulings could set parameters on presidential authority
By Lawrence Hurley
WASHINGTON, May 5 (Reuters) - Congressional Republicans who strenuously objected when a Democratic-led U.S. House of Representatives panel subpoenaed President Donald Trump's financial records last year have remained unusually quiet now that the fight has reached the Supreme Court.
Representative Jim Jordan, the House Oversight and Reform Committee's senior Republican, described the move in an April 15, 2019, letter as "an unprecedented abuse of the committee's subpoena authority to target and expose the private financial information of the president of the United States."
But neither Jordan nor other Trump allies in Congress or in state capitals have weighed in on the Republican president's legal effort to block enforcement of the subpoena, which was issued to his long-time accounting firm Mazars LLP.
The case has been consolidated with another one in which Trump is seeking to prevent enforcement of separate subpoenas from the House Intelligence and Financial Services Committees targeting his financial records from Deutsche Bank AG and Capital One Financial Corp.
The justices will hear arguments on May 12 in those cases and a third one seeking similar records. Rulings are expected by the end of June, ahead of the Nov. 3 election in which Trump is seeking a second term.
The third case involves Trump's effort to block a subpoena issued to Mazars as part of the Manhattan district attorney's criminal investigation of the president and his family real estate business.
Unlike in other politically charged cases, his high-profile allies in Congress and in Republican-governed states like Texas have not filed amicus - so-called friend-of-the-court - briefs in support of Trump with the Supreme Court. His only major supporter is his own U.S. Justice Department.
Such briefs are an avenue to express formal legal support and furnish information to influence the court's decision-making.
Jordan did not provide comment for this story. A House Republican aide said congressional Republicans see the dispute as between Democrats and Trump.
"Republicans trust the court to get the balance right between the investigatory prerogatives of Congress and the privileges that the Constitution bestows on the president," the aide said, speaking on condition of anonymity.
Unlike other recent presidents, Trump has refused to make public his tax returns and other financial records. His lawyers have argued that the U.S. Constitution gives a president sweeping protection from scrutiny by Congress, prosecutors and the judiciary.
The rulings by the Supreme Court, whose 5-4 conservative majority includes two Trump-appointed justices, could help set the parameters for presidential authority.
Michael Stern, who served as a House lawyer when it was under Republican control, said it is "striking that for whatever reason they declined to participate," referring to Republican lawmakers.
Jay Sekulow, one of Trump's personal lawyers, said he was pleased to have the support of Justice Department briefs but declined to comment further on amicus brief strategy in the cases.
In major politically divisive disputes at the court, there are often dozens of briefs filed on each side.
In the consolidated congressional subpoenas cases, just six briefs support Trump, including the Justice Department's. The others are from lesser-known conservative groups and individuals. House Democrats mustered 15 supportive briefs. In the New York case, three briefs back Trump and 10 oppose his stance.
In all three cases, those filing briefs opposing Trump included Republican former lawmakers and senior figures in previous presidential administrations.
Tom Coleman, a Republican former congressman from Missouri who left office in 1993, said in an interview he was concerned about the broad assertions of presidential power by Trump's lawyers.
"To say the president is unaccountable to anyone and can do whatever he wants and is above the law is pretty head-spinning," Coleman said.
The House Oversight Committee said it needed the subpoenaed documents for its investigation into whether Trump inflated or deflated financial statements for potentially improper purposes.
Veterans of similar constitutional showdowns note that the current arguments in support of Trump could backfire when Republicans next control the House and want to investigate a Democratic president. It was unclear whether that factored in Republicans staying on the sidelines.
In past court battles between branches of government, individual lawmakers have weighed in.
In 2008 during Republican President George W. Bush's administration, House Judiciary Committee Republicans filed a brief in federal court opposing efforts by the Democratic-led House to force former White House lawyer Harriet Miers to testify.
Four years later, Democratic House members filed a similar brief backing Democratic President Barack Obama's administration when the Republican-controlled House sought documents involving a botched gun-trafficking investigation known as "Fast and Furious."
Neither of those cases reached the Supreme Court.
State leaders often weigh in on contentious matters. Texas Attorney General Ken Paxton, a Republican, often pursued legal challenges to Obama policy moves and has sided with Trump in multiple cases. Paxton has remained on the sidelines of the Trump financial records dispute. A Paxton spokesperson declined to comment.
In the New York case, 15 states led by Virginia filed a brief backing the subpoena. No states backed Trump.
Chicago-Kent College of Law professor Carolyn Shapiro said states are unlikely to argue in favor of limits on state power especially with the New York subpoena seeking documents from a third party, not the president himself.
"I could imagine," Shapiro said, "that the state line-up might be different if it were an investigation into the president's own official conduct."
Reporting by Lawrence Hurley; Additional reporting by Karen Freifeld; Editing by Will Dunham