If such a thing would happen, Trump might seek expanded presidential powers as if the country was at war.
Suspension of habeas corpus might result, meaning people could be held in unlimited detention without charges. Domestic warrantless surveillance could be expanded. Lawful immigrants could be detained. The posse comitatus rule could be waived, allowing the military to act as police.
Trump already appears to be fanning public opinion by complaining about past terrorist acts that never existed. Earlier this week, Trump falsely charged the media with covering up terrorist attacks that never actually occurred.
Such behavior isn't typical for a president, but it is for a dictator.
As Lizza's piece also mentions, Trump has been openly attacking judges, which may be setting the stage for him later totally ignoring court orders he doesn't like. This would throw the country into a constitutional crisis.
One might be tempted to accuse Lizza of overreacting, and his article seems to anticipate such a charge. The piece quotes several prominent Republicans and conservatives who are deeply concerned about what they see in Trump and the dark place he appears to be taking the country.
If conservatives and Republicans are worried about where the President from their own party is headed, that's not an alarm moderates, progressives, and liberals can ignore.