Congressional Democrats and the Trump administration are headed for a legal showdown after House Ways and Means Committee Chairman Richard Neal imposed an April 23 deadline for the documents. The IRS has already missed the April 10 deadline Neal set in his initial request.
Congressional Republicans, meanwhile, have said little, fearful of going up against a president popular with their base.
"He said Treasury respects lawmakers' oversight duties and could make sure taxpayer protections would be" scrupulously observed, consistent with my statutory duties" because the section reviews the request.
Neal also wrote that concerns about the committee's access to the returns were "baseless".
Other Omar critics have focused exclusively on that one single line, accusing her of trivializing the inhumanity of September 11 but not mentioning the rest of her speech.
Mnuchin says he needs more time to review the request.
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He said the department would probably respond by Mr Neal's deadline but did not say whether he would provide the returns as demanded.
Mnuchin told the media on Saturday that he was trying to move carefully in overseeing a request that raises "very, very complicated" legal questions, emphasising that his decision could have long-lasting repercussions for future requests by Congress to the IRS.
Trump has repeatedly refused to publicly release his tax returns or send them to Congress. But opponents, mostly in the Democratic Party, say his push for building more walls on the Mexican border and his nearly daily denunciations of migrants as unsafe criminals incites racial hatred.
Nadler said Trump has "no moral authority" for talking about September 11. "Frankly, the people don't care".
"The president has told people close to him that the attempt to receive his returns were an invasion of his privacy and a further example of the Democratic-led" witch hunt" - that he's called special counsel Robert Mueller's investigation - meant to damage him.
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President Donald Trump is pictured walking to Marine One.
Democrats do not expect the Treasury to comply but they have not sketched out their next steps. Neal's request for the returns of a sitting president is unprecedented, and legal experts say its success or failure may depend on a court ruling about the committee's legislative objective for seeking the documents.
If Mazars refuses to comply with the subpoena, the matter would likely go before a court, which would determine whether the Committee has a legitimate legislative objective in seeking the documents. Nonetheless, the Commissioner retained his defense that Treasury supervises the IRS.
"Certainly, we're looking at all options", Sanders said during an appearance on "Fox News Sunday".
Chairman Neal asserts his right to request the returns under Internal Revenue Code section 6103 (f), to ask for any tax return from anybody from the IRS.
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