Marc Thiessen All of Washington is focused on the political peril President Trump faces from Robert Mueller’s investigation. But the Mueller probe could very well turn out to be a disaster, not for Trump, but for the Democrats. The special counsel was appointed to investigate whether Trump engaged in a criminal conspiracy with Russia to win the 2016 presidential election. If Mueller finds incontrovertible evidence of a criminal conspiracy between Trump and Russian President Vladimir Putin, then the president will be — and should be — removed from office. But…