Someone else here on DU alerted me to the Russian apartment building bombings in 1999 that led to Putin's rise. Apparently, President Yeltsin looked like he was going to lose the election, so, it is speculated, Putin and the Russian Federal Security Commision (FSC) blew up some apartment buildings and blamed it on Chechan terrorists. The bombings sowed enough terror, chaos, and confusion that Yeltsin got elected. When Yeltsin got kicked out for corruption, Putin took over. Here's an article about all that from Business Insider:
[link:https://www.businessinsider.com/how-the-1999-russian-apartment-bombings-led-to-putins-rise-to-power-2018-3|
Russian involvement seems possible due to the recent massive Russian hacking, as drray23 points out.
Also, the Nashville bombing seems too calculated and sophisticated for Trump's followers to have been able to carry out.
Could be wrong. Could just be an intelligent lone wolf like Ted Kaczynski. Apparently they have a "person of interest." See where that leads.