The intelligence whistleblower whose complaint has triggered an impeachment showdown says the Trump administration abused a highly classified computer system in order to hide President Trump’s attempts to get dirt on Joe Biden’s family from Ukraine’s president. So what kind of damage can using national security resources for political purposes cause and how often does this kind of thing happen?

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The heart of the whistleblower’s allegation is that Trump officials took a document of middling classification level and stashed it in a computer system designed to protect some of the country’s most sensitive secrets.