The ramp-up in political spending across Facebook’s social networks, which also include Instagram, is breathtaking: In 2014, digital ad spending was 1% of all political ad spending. Now it’s 22%, or about $1.9 billion, according to the nonpartisan Center for Responsive Politics. Facebook says that politicians have spent nearly $300 million in the US on Facebook ads since May.

And

Politicians who want to reach the same voters their competitors are reaching on Facebook have little choice but to go there, too.

Which helps explain why Facebook was so willing to censor conservative political ads.