See this article from Forbes Magazine https://www.forbes.com/sites/victorlipman/2013/04/25/the-disturbing-link-between-psychopathy-and-leadership/#5a8c0dcc4104 which is quoting an academic study published by National Centre for Biotechnology Information, U.S. National Library of Medicine, https://www.ncbi.nlm.nih.gov/pubmed/20422644. The actual finding is that there is 1% occurrence of psychopathy in the general population but this rises to 3% amongst senior execs. It seems highly likely to me that this would also apply to people who reach the top in politics, possibly more so given what it takes to get there.
Part 2 Assess - Timeline - Present - Limited Participation and Disengagement - The structure of disengagement