UPDATED: Shares of Twitter took a nosedive in early trading Monday, coming after the social network permanently banned Donald Trump — its highest-profile user — prompting worries that would hurt user and revenue growth.

Twitter’s stock dropped as much as 12% at the market open Jan. 11. It recovered somewhat from that to end the day down 6.4%, to $48.18 per share. The decline comes after Twitter shares had a 37% run-up in the last two months of 2020. Shares of Facebook, which suspended Trump’s Facebook and Instagram accounts and has no plans to unfreeze them, fell 4% Monday. The Dow dropped 0.3% for the day and the Nasdaq Composite declined 1.25%.

Investors view Twitter’s booting of Trump, along with the removal of other right-wing accounts, as a potential drag on user growth going into 2021. On Friday afternoon, Twitter issued a permanent ban on Trump, citing his repeated violation of the rules and risks that the outgoing president could incite further violence after the deadly riot at the U.S. Capitol on Jan. 6.

Just as media investors were quick to short Fox Corp.’s stock post-election over fears Fox News Channel will suffer lower viewership after Trump’s loss, Twitter is similarly at risk, MoffettNathanson senior analyst Michael Nathanson suggested in a research note Monday.

Twitter’s daily active users in the U.S. “are still very small and at risk of stalling” with Trump’s exile from the platform, Nathanson wrote. “We have always wondered how much of Twitter’s growth came from the ‘Trump Bump’… Now we will find out.”

Despite a risk of “churn from the conservative community” for Twitter, “strong political activists will stay on Twitter for other content,” Bank of America analyst Justin Post wrote in a research note Monday, retaining a “buy” rating on the stock. In addition, “we think other Tweeters can replace Trump,” he opined, noting that president-elect Joe Biden’s Twitter account has added more than 4 million followers since he was confirmed as the winner of the 2020 election in mid-November.

In the fourth quarter, Twitter’s stock climbed over an expected bump in 2021 brand advertising, and the return of events like the Tokyo Summer Olympics and the NCAA men’s basketball championship, Nathanson noted. But at the same time the company faces increased regulatory risks, and Twitter continues to trail competitors like Facebook in monetizing its user base, the analyst wrote.

Twitter is scheduled to report Q4 2020 results on Feb. 9 after the market closes. The company had issued an uncertain ad forecast for the last three months of the year, telling investors in late October, “As we approach the U.S. election… it is hard to predict how advertiser behavior could change,” noting that in the second quarter of 2020 many brands “slowed or paused” spending in reaction to protests and civil unrest in the U.S.