You don't need the internet, it's been done for centuries. It is a derivative of mimesis which is biologically encoded colloquially as 'monkey see, monkey do'. You don't even need espionage to influence group think dynamics and mass hysteria. Want to start a stampede? Start running fast away from a group of people.

Trump is the poster boy for transmitting disinformation. The solution is to teach and promote critical thinking but that has been weaponized into 'do your own research' which conveniently neglects to do the critical thinking component that research requires.