The law is clear that all federal employees must follow tax code law. Failure to act imposes mandatory firing, a possible fine and possible jail time up to 5 years. The 8 minute segment explains why Secretary Mnuchin and IRS Commissioner Charles Rettig are being very, very careful to say they are following the law when faced with a legal demand from the House of Representatives to see the last six years of Trump's tax returns.
Neither President Trump, Mnuchin nor Retting want to release Trump's tax returns. They just can't say they refuse to comply with the legal House request without facing mandatory firing from the federal government and a possible fine and jail time. Trump's advisers are no doubt telling Trump to keep his mouth tightly shut and let other people fall on their swords if it comes to that.
The apparent ways forward for this include: