TL;DR; Lula was the clear favorite for the 2018 election. In a rush job, a new law passed lowering the bar one takes to be arrested (you can be arrested in your second instance instead of going to the Supreme Court if you had a case) and raised the bar on who could run for the office. At the same time, in a Record time, Lula was convicted in the first and second Court instances (by a judge that by "coincidence" took the role of Minister of Justice for Bolsonaro and was declared as suspect in the case because the cooperated with the prosecution) and was declared ineligible. In a shitshow, the establishment right didn't put forth a good candidate, Bolsonaro, then a whacky low tier congressman most famous by appearing in sensationalist night time talk shows took these votes among with the authoritarian right voters and won against Haddad, the left leaning guy subbing for Lula, but was less popular and charismatic. In the last 4 years every accusation against him dropped and now here we are.