With Facebook and Twitter at the center of national conversations about political ad transparency and fake news, the year ahead will be anything but dull for social media companies.

Facebook’s growing dominance of digital is already well-known; this year it will account for 23.0% total US digital ad spending. But it will also hit a new height in 2018, taking in $1 of every $10 spent on all advertising—digital and nondigital combined.

To put an even bigger emphasis on that point, Facebook’s US ad revenues (forecast by eMarketer to reach $21.57 billion this year) will be twice the amount spent on newspaper advertising ($10.74 billion) and nearly as much as advertisers will spend on the entire print category ($23.12 billion). In 2019 Facebook will zoom ahead, accounting for 11.3% of all US ad spending, compared with 10.0% for print.

Meanwhile, Twitter and Snapchat will reach parity in US ad revenues.

eMarketer expects Snapchat to pull in $1.18 billion in US ad revenues this year, vs. $1.16 billion for Twitter. Although Snapchat’s user base is growing more slowly than expected, it will still see ad revenue growth this year, thanks to improved measurement capabilities and a growing embrace of ad targeting tools.

Twitter, on the other hand, is not growing: Its ad revenues are expected to drop by 4.5% in 2018. Despite its push into video programming, Twitter will continue to eke out only marginal gains in usage, making for revenue challenges as well.

These forecasts are drawn from eMarketer's latest report, "US Social Trends for 2018: eMarketer's Predictions for the Year." The report looks at key eMarketer forecasts for the year ahead and examines our 2017 predictions—what we got right as well as what we got wrong. eMarketer PRO subscribers can access the full report here. Nonsubscribers can learn more here.

In the latest episode of "Behind the Numbers," eMarketer analyst Debra Aho Williamson takes a peek into the future and predicts what will happen in the fast-changing space in 2018.