Their testimony during the impeachment hearings does not change this calculus. Employees who file complaints pursuant to the Whistleblower Protection Act are protected from retaliatory personnel actions. This is why the identity of the whistleblower, whose letter helped initiate the entire imbroglio, has not been disclosed and why he or she has not been punished. Congress could extend whistleblower protection to people whose testimony is compelled pursuant to a congressional investigation, but it has not. Until it does, Trump is free to act as he wishes.
The idea that Trump’s acts could chill other White House officials from coming forward to spill the beans on their boss is laughable. People don’t just end up working in the White House. They are highly ambitious, career-focused men and women who have weighed the pros and cons of working for any particular person. I know many highly qualified conservatives who chose not to work in the Trump administration because even their ambition could not impel them to work for a man whom they distrusted or despised. People who made different choices knew what they were doing when they signed up and are highly unlikely to want to risk their careers anyway. Vindman’s reassignment simply tells them what they already knew.