Well, Now, This is Kind of a Rookie Mistake in Strategic Political Thinking ...

Writing at The Atlantic, Alexis C. Madrigal calls 2018 "The Facebook Election That Wasn't."

Campaigns have spent $3 billion on TV and radio, doubling their spending from 2014. The dueling campaigns for one of Florida’s Senate seats and for the state’s governorship alone have plowed $354 million onto the airwaves. According to Facebook’s Ad Archive Report, that’s almost exactly what all political advertisers combined spent on the platform from May to November 3. We might have spent the past two years talking about Facebook’s electoral impact, but the people with skin in the game are betting it is about a tenth as important as TV and radio.

How much was spent on one thing versus another, in and of itself, tells us very little about how "important" either thing is.

There are a bunch of different ways to reach voters. Some of those ways reach the same voters as others. Some of those ways reach different voters than others. Some reach more voters more times at the same cost.

If it costs me $1 to reach a voter using Facebook, $2 to reach that same voter with a piece of direct mail, and $3 to reach that same voter with a radio or television ad, it does not follow that because I spent $1, $2, and $3 on those things respectively that the last one is "more important." It just means that I spent what I had to spend to reach that voter via each medium.

And it may cost me $1 to reach that voter 10 times, rather than one time, via Facebook (and to reach 100 other voters because that voter shares it with all his friends) and $30 to reach that same voter 10 times by radio or television. Should I multiply my Facebook spending by 30 just to show that I consider Facebook "important" even if I don't need the additional repetitions?

I would say that the last part is very relevant. If I get a flier in the mail, I probably don't run over to show it to my neighbor. If I see an ad on television, I probably don't DVR it and invite everyone I know over to watch it. But if I see an interesting piece on Facebook, I might well "share" it to my ~5,000 "Facebook friends" and 100 of them may take a look at it.

Social media is cheaper, but that doesn't mean it's less "important."

If you're a voter, ask yourself this: Which affected your thinking about the various candidates more -- TV ads or memes your friends threw at you on Facebook?