While it is certainly problematic it doesn't change the fact that the fault is ultimately with the voters and their lack of critical thinking and evaluation skills which makes it effective.

The scenario is akin to computer security. Sure it is wrong for a hacker to manipulate flaws in the system enmasse but the underlying susceptibility to the bullshit is the root cause. Even if you stop that bad actor the root cause remains open to all with evil intent.

If I were to spend trillions on the worst political campaign - say "lets ban the anti-retrovials and give everyone AIDS" in a remotely sane electorate I would have essentially zero impact other than the massive reputational damage I would take. In a terrifyingly insane one where the worst casually proposed idea achieved 100% acceptance the entire populace would be dead without outside military intervention.

Fixing it is easier said than done but would involve education and deep investment in critical thinking.

What is special about this day and age? For reasons of manipulation of large numbers of people, this has always been true. He who controls the present controls the past, and he who controls the past controls the future.