Both Trump and Johnson are evasive shallow individuals. Johnson appears to be a puppet of the Vote Leave operation, he avoids serious questions related to Brexit and his government has suppressed many facts. They have denied a democratic revisit of Brexit, back in 2016 they didn't expect to win so had no viable plan, they still have no viable plan. Boris rules by Sound Bites with little substance behind them.
Trump is a different character, though sound bites like "America First" do attract disaffected voters just as "Get Brexit Done" does over here. However, elections in both countries have evidence of outside interference coupled with outdated electoral systems. Opposition is stifled, protests disregarded, and it is always someone else's fault. Let's blame China or the EU and not recognise our own fallibility.