Mueller investigation cost
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There have been many reports that the Mueller (Special Counsel) Investigation cost the taxpayers many millions of dollars. What is the best available information about its cost?

Trump and Mueller
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Donald Trump expressed concern that the Mueller investigation was biased against him because there were 13 Democrats (either registered as Democratic, or donated to Democratic Party candidates) and no registered Republicans among its investigators. Are these concerns reasonable?
Trump and Mueller
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Donald Trump tweeted:

How accurate are these assertions?

Robert Mueller
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For the years during which the Russia Investigation took place, there were concerns raised that the investigation itself was unconstitutional. Was it?

Robert Mueller
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This argument map explores the best reasons to believe that the "Steele dossier" was what began "the Mueller investigation".