Has Trump Derailed the Mueller investigation?

THE WORST THING about Trump pardoning the racist Arizona sheriff Arpaio is that his doing so may impede the special investigation being conducted by Robert Mueller to determine if Trump and his associates were in collusion with the Russians to distort the 2016 election. 

By pardoning the Arizona sheriff Trump has effectively signaled Paul Manafort, Michael Flynn and other apparent Russian-collusives that they don't need to trade information to Mueller in exchange for immunity. Trump's pardons can give them immunity. They don't even have to respond to Mueller's court-issued subpoenas or else face contempt of court charges. The sheriff was on his way to jail for defying a court order, and Trump's pardon spared him being jailed for contempt of court. Let's hope Mueller can make his case without the testimony of Trump's associates, accountants, etc.