Beginning in 2016, former and currently serving US intelligence officers, mainly from the Central Intelligence Agency (CIA), conducted a major political campaign featuring public commentary and leaks designed to thwart the presidential candidacy, and then the presidency, of Donald Trump. This "politicization" of intelligence, which traditionally is defined as the injection of personal or organizational perspectives into intelligence products to serve personal, ideological, or organizational interests of intelligence officers, reflected a remarkable change from the once-strong CIA ethos of apolitical public service. This book describes the startling political activism of intelligence officers in recent years, identifies its causes, and evaluates its many negative consequences. Most importantly, the activists damaged the credibility of US intelligence in the eyes of Trump Administration officials and undoubtedly many future senior national leaders, thereby eroding the trust in intelligence that decision-makers must have if they are to use intelligence effectively. Although the overt activism subsided in 2021, the Biden administration has not addressed its causes. The evident success of activists in helping to defeat Trump in 2020 surely has emboldened some intelligence officers, who remain poised to attack presidential candidates whose political views they dislike. This book also identifies actions needed to address this significant threat to American democracy.