Sanders also defended Trump when Stephanopoulos pointed out that some had accused the president's tweets of inciting anti-Muslim violence against her.
"Those conversation have started, but it would be premature for me to conclude how long that will take, because as I've said these are complicated issues", said Mnuchin, who was speaking on the sidelines of the annual International Monetary Fund meeting in Washington.
On Saturday, Neal said the administration has no right "to question or second guess" his motivations.
Sanders appears on ABC's This Week and Fox News Sunday.
"I am aware that concerns have been raised regarding my request and the authority of the Committee", House Ways and Means Committee Chairman Richard Neal said in a letter to Internal Revenue Service Commissioner Charles Rettig after an initial April 10 deadline lapsed.
After reports said the Trump administration had twice considered and rejected a plan to bus illegal immigrants to sanctuary cities to retaliate against his political foes, the president embraced the idea on Friday.
SpaceX successfully lands all three Falcon Heavy boosters
All three of the rocket's boosters safely landed on Earth; the side boosters for this launch hadn't previously been used. This Falcon Heavy was also a next-generation version using the Falcon 9 Block 5 boosters for the first time.
Department of Homeland Security officials were reported to have pushed back against the transfers of detained migrants as illegal, impractical and counter-productive.
Press secretary Sarah Sanders added that Trump wished no "ill will" upon the Muslim congresswoman.
Neal said that the Committee is "considering legislative proposals and conducting oversight related to our Federal tax laws, including, but not limited to, the extent to which the IRS audits and enforces the Federal tax laws against a President".
Democrats want Trump's tax returns as part of their investigations of possible conflicts of interest posed by his continued ownership of extensive business interests, even as he serves the public as president.
Several Republicans have tried to navigate around Trump's illegal "sanctuary city" suggestion, including one of his most staunch defenders, New York Republican Peter King. She said she hopes Democrats will work with the president on a comprehensive immigration bill.
The transportation of migrants arrested at the border to large and faraway cities would be burdensome and costly at a time when Immigration and Customs Enforcement (Ice) is stretched thin, having released over 125,000 migrants pending their immigration court date since 21 December.
"People have come to this country, documented or undocumented, they're hard working and family people, they want a better life", said Philadelphia Mayor Jim Kenney, according to KYW Radio. They create businesses and jobs. "If they reverse the decision and send people here, I'd be happy to have them".