Facebook's analysis of the sentiment of users talking about Hillary Clinton shows a gradual but marked downturn in the tone of conversation about the presumptive Democratic candidate as the 2016 campaign approaches.

The share of conversation about Clinton that was positive dipped from 57% during one period in the fall to 52% in January and then a 50% average in February. By Feb. 28, that sentiment turned negative, and has stayed largely more negative than positive as conversations multiplied amid debate over her use of a personal email account.

The sentiment data is drawn from a Facebook project that analyzes the language and symbols used by the massive social networks users. (You can read more about the project here.) The data has been shared with BuzzFeed News in a partnership with Facebook.

The sentiment data may not mirror polling data, though it has so far roughly tracked public polls. Her favorability rating has gradually declined, from peak over 60% in 2010, to below 50%, according to a recent New York Times average of public polls.

And the sentiment data also offers a glimpse at how the under-the-surface conversation about Clinton may shift, despite the challenge — for both Clinton and her Republican foes — of changing public opinion about so well-known a person.

Last week, the news of her family's foundation quietly accepting foreign donations was followed by news that Clinton exclusively used personal email while at the State Department on Monday. Reports that Clinton used a private server located in her own home followed. Questions remain about how Clinton's staff selected email to be sent to the State Department, whether her email was sufficiently secured during her tenure there, and whether Obama administration officials ever told Clinton or her senior aides to stop using the account.

Those stories caused a huge, sustained spike in the number of Facebook interactions about Clinton.

But even before the story broke, the sentiment around her had dipped from earlier this year — and was in the upper 40s in terms of positive sentiment.