If you don't want to know how easy it is for a canny individual - or a malicious state actor - to hack into the electronic voting technology used in the U.S., don't watch Kill Chain: The Cyber War on America's Elections. In this unnervingly persuasive HBO documentary, directors Simon Ardizzone, Russell Michaels and Sarah Teale marshal cyber-security experts, statisticians and lawmakers to expose cracks in the system that could easily allow hackers to affect voting results. The filmmakers' sources also include actual hackers, among them an individual who breached Alaska's voting system in 2016 just to see if he could. One of the central figures of Kill Chain is election-security expert Harri Hursti, who explains, with clarity, just how vulnerable American voting systems are. Although voting machines are supposed to be kept in secure facilities, Hursti found a widely used model for sale - on eBay. The vendor had hundreds of them. Hursti bought a few, using them to explain how easily their workings could be examined and breached. He also brought a selection of voting machines to Def Con, a three-day conference for hackers, and invited attendees to go at them; one expert quickly figured out how to shut down a machine remotely from a laptop. The U.S. voting system is, as several interviewees in Kill Chain put it, a bipartisan concern; still, as the documentary notes, Senate majority leader Mitch McConnell has blocked votes on the Secure Elections Act and four similar bipartisan bills.