Actively, publicly and legislatively support whistleblowers, civil disobedience against illegal orders, and resistance in the executive branch.
Support and pass legislation to immunize any government worker who complies with a congressional subpeona in defiance of their bosses
Start getting promises from Dem Presidential candidates to pardon anyone who gives information relevant to oversight to Congress, even if doing so is in violations of the law.
Set up a special committee to aid any government worker willing to resist an illegal order, with access to lawyers/public unions/other groups to provide aid and information.
In short, support the resistance in the executive branch fully, publicly and without reservation.