(Adds background on Trump's attorney response)
WASHINGTON, April 7 (Reuters) - President Donald Trump's tax returns will never be handed over to Democratic lawmakers, White House Chief of Staff Mick Mulvaney said on Sunday, defying an effort in Congress to learn more about the Republican leader's personal finances.
Asked on "Fox News Sunday" if congressional Democrats will succeed in obtaining Trump's tax returns, Mulvaney said: "Never. Nor should they."
He dismissed an effort to obtain the returns, launched formally on Wednesday by U.S. House of Representatives tax committee Chairman Richard Neal, as a political ploy from Democrats who will never stop attacking Trump.
“Democrats are demanding that the IRS turn over the documents. That is not going to happen, and they know it. This is a political stunt,” Mulvaney said.
Democrats fired back that Neal's request to the Treasury Department for Trump's returns is grounded in law and a needed inquiry, given Trump's refusal to disclose his tax records and to divest himself of his business interests.
"This is a legitimate authority that the Congress has. This president, by the way, is the least transparent president that we've had in half a century," Democratic Representative Dan Kildee, a tax committee member, told ABC's "This Week."
"It is not up to President Trump, it is not up to some lawyer that President Trump hires, to determine whether" his tax returns can be sought, Kildee said. "This is not an autocracy. The president does not get to decide for himself and for Congress what a legitimate subject of inquiry might be."
An attorney for Trump on Friday blasted House Democrats' request for six years of Trump's personal and business returns as "a misguided attempt" to politicize the tax laws, accusing lawmakers of harassment and interference in IRS audits.
In a statement that mapped out the legal battlefield ahead, Trump lawyer William Consovoy said the request filed by Neal flouts "constitutional constraints."
One of many investigations targeting Trump on Capitol Hill and in the U.S. court system, the House Democrats' probe into the president's tax returns could pull back the curtain on his business empire and his reputation as a dealmaker.
Unlike previous presidents over recent decades, Trump has refused to make public past tax returns, while retaining ownership in many enterprises, ranging from golf courses and hotels to Trump Tower in New York and Mar-a-Lago in Florida.
(Reporting by Doina Chiacu and Kevin Drawbaugh Editing by Phil Berlowitz and Lisa Shumaker)