Less than .3% separated Hillary Clinton and Bernie Sanders in yesterday’s Iowa caucuses. Hillary Clinton took 49.9% of votes while Bernie Sanders squeezed in behind with 49.6%. It hasn’t been this close in years: in 2008, Obama won in Iowa 10 percentage points ahead of Clinton.

The Iowa caucuses have a 43% success rate of predicting the Democratic nominee for President. In this election, the race seems too close to call. Can social media act as a tie-breaker between Hillary and Bernie, and help predict who will win the nomination?

The Few, the Engaged

In 2015, Secretary of State Hillary Clinton was believed to be a shoe-in for the nomination. She was endorsed last week by The New York Times’ editorial board as the better option (“one of the most broadly and deeply qualified presidential candidates in modern history”).

But Bernie Sanders, considered an underdog in 2015, has the same outsider’s appeal on the Democrat side as Trump has for Republicans. As discovered using Crowdbabble‘s analytics engine, Sanders’ fanbase on Twitter, Instagram, and Facebook has been expanding more quickly since the January 17 debate. The Vermont senator’s engagement rate — the percentage of followers who like, comment, or share each of his posts — is higher overall.

Below, Sanders’ engagement rates on Facebook, Twitter, and Instagram, as found in Crowdbabble. The senator’s followers are substantially more engaged than Clinton’s on Instagram and Twitter.

Hillary’s engagement rate on Facebook has slid since the January 17 debate, but her Page fans are more active than Bernie’s.

On Facebook, the Clinton campaign is working harder. Hillary has posted 101 times since January 25, while the Sanders campaign has posted 38 times.

Below, a collection of statistics on Bernie and Hillary’s performance over the past week, collected in Crowdbabble:

Clinton also attracted four times the comments, sparking debate and attracting support from her fans. Sanders experienced a much larger jump in followers, surging ahead of Clinton on the platform.

A Maybe-Unbeatable Lead

Bernie Sanders’ followers are more active, spreading his campaign within their own social networks more often and more widely. Is Clinton’s online following growing quickly enough to compensate for her low engagement rate?

Sanders has pulled ahead of Clinton on Facebook by more than 100,000 fans. On Instagram, he’s also catching up. Below, a Crowdbabble visualization of Sanders’ growth rate on Instagram, where he now has 672,000 followers:

As with Facebook, Sanders’ growth on Instagram is volatile.

Clinton has slowed down on Instagram, gaining 4,163 followers per day to Sanders’ 5,035. As shown in the Crowdbabble graph below, however, her growth rate on the platform seems less vulnerable to sudden dips:

Hillary’s 10k leap during the Iowa caucuses suggests that she could maintain her lead on Instagram, if her followers become more active. With a faster growth rate and higher engagement rate, @BernieSanders is projected to rise above Hillary’s 760,000 followers on the platform.

Clinton is furthest in front on Twitter, with 4 million more followers than Sanders. On Twitter, Sanders’ following will likely stay substantially smaller than Clinton’s. Sanders gains 6,209 new followers per day, while Hillary gains 6,562. Aside from engagement rate and follower base, there’s also total reach to consider: on the whole, Clinton’s Twitter followers are less engaged, but seem to have larger followings themselves. The candidates’ most engaged followers on Twitter — the accounts that like, comment on, and retweet their content the most — are shown below:

Not having influencers actively engage with his tweets appears to be an error in strategy on Bernie’s part, as the Sanders campaign does have many offshoot accounts with large followings. On Twitter, Clinton’s lower engagement rate might go further.

On Facebook, Sanders has gained a comfortable lead in people engaged and total fans. As shown in the Crowdbabble graph below, Sanders’ growth rate on Facebook leading up to the Iowa caucuses has been volatile, but strong:

On Facebook, Bernie was behind until this week: now he’s more than 100,000 fans in front of Hillary. If his engagement rate stays above 110% on some platforms, Bernie’s momentum on social media could snowball. His formidable lead in engagement rate might slowly turn into a lead in fans and followers on Facebook and Instagram.

Slow and Steady Wins the Race?

In 2008, slow and steady growth wasn’t enough to secure a win for Hillary in the Iowa caucuses. But in 2016, it might be enough.

If Hillary’s large following becomes more active online, the total number of people engaged would quickly eclipse Bernie’s more active but smaller fanbase. When accounting for the size of the candidate’s follower bases, Bernie’s lead seems less certain.

Though Sanders’ engagement rate is five times higher, the number of people engaged per post is closer to Clinton’s number. With 5.28 million Twitter followers, a 7% engagement rate means that about 369,000 followers actively engage with @HillaryClinton per post on the platform. 624,000 followers actively engage with @BernieSanders, with its 1.3 million followers and 48% engagement rate. A small 5% uptick in engagement for Hillary on Twitter would push her number of active followers on the platform to 633,000, ahead of Bernie’s 624,000.

With millions more followers on Twitter, Hillary has the largest following on social media. The former Secretary of State has a much bigger audience for her campaign, but fewer active participants than one might expect. But both candidates have far more active follower bases than they did two weeks ago: since January 17, engagement on Twitter and Instagram has more than quadrupled for both candidates.

If Bernie’s followings keep rising at their current rate, the Vermont senator will maintain his lead on Facebook and overtake Hillary on Instagram.

There seems to be a strong correlation between Bernie Sanders’ rapid growth on social media and his leap forward in the polls to a near-tie in Iowa. Engagement rate seems to be tied more closely to poll numbers than share of total followers. With that correlation in mind, Bernie appears poised to win the nomination with a much more active, faster-growing following online. But it would only take a small shift in engagement for Hillary to energize her much larger following and secure the nomination.

All data visualizations made in Crowdbabble. This post is part of a series on the Presidential Election 2016 and social media. Look for election here.