Well, you consider it to be cheap and effective -- in 2018.

But back in 2016: Obama said there was “no serious” person who would suggest it was possible to rig American elections, adding, “I’d invite Mr. Trump to stop whining and go try to make his case to get votes.” [0]

I wonder how public opinion shifted. Back in 2016, the idea of rigging elections with facebook ads was alex-jones-level of tinfoil conspiracy, and now we are discussing it as an obvious, cheap and effective tactic.

[0] https://www.reuters.com/article/us-usa-election/obama-tells-...