--what would be the minimum, viable path to WW3 from the current conditions
Continuing to elect and hold with high regard the neocons (H. Clinton, Lindsey Graham, Cheney, Biden, Obama, McCain), conversely getting rid of the peacemakers (Trump, Carter, Nixon, Reagan, Tulsi Gabbard). Also giving those neocons strong mandates for war mongering. Voters get who they vote for and as the biggest military, US leadership is important to whether we will see WW3. At present, a specific path for the warmongers is to escalate Israel fighting with Palastines into a serious escalation with Iran. Its what these people do best....like setting up the Ukraine war after they reneged on pledges Clinton made to Russia. And another thing to remember is after Iran gets started...even the sane non war mongering politicians will be clammering for WW3 and flipping down dominoes when all else fails.
There are 2 very big differences now and back during 1940. Back in 1940 the only war monger was Roosevelt who was kept at bay staying out of Europe because people like Lindberg were successful convincing peace to the public. The US at that point was much more pacifist and neutral than it is today. But the biggest other difference is the nuclear weapons and other bio and tech devices that can destroy all lot of humanity in a real short order. Weapons that can destroy all of humanity make no sense because at best they cannot be used, yet their existence threatens the life of the planet. So why have them? Accident, emotional response, loss of reason are all human faults that can come into play at any time. Not to mention a software glitch during a period of high alert.