Trump rally Manuel Balce Ceneta/AP Photo

James Barnes, a former Facebook employee who was key to implementing Donald Trump’s online advertising campaign, is now working to prevent the president’s reelection, according to The Wall Street Journal.

The Journal’s Deepa Seetharaman detailed Barnes‘ involvement with the Republican party and how his discontent with Facebook’s political advertising practices ultimately led to his departure this spring.

Facebook has signaled that it would make changes to its advertising tools amid criticism that the social media giant lets politicians lie in ads.

Twitter announced last month that it would ban most forms of political advertising.

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A former Facebook employee who was instrumental in shaping President Donald Trump’s online advertising campaign in 2016 is now working to avert his reelection.

In a Saturday feature, The Wall Street Journal’s Deepa Seetharaman detailed how James Barnes became jaded by Facebook’s work with the Republican party and Trump’s political rhetoric. The story was based on three weeks of interviews with Barnes and sheds more light on Facebook’s role in the 2016 election.

The social media giant has been implicated in revelations that Russian operatives tried to influence the election outcome by buying ads on the platform. Unlike Twitter, Facebook has not banned most forms of political advertising despite criticism that it gives politicians a huge platform to spread misinformation.

According to the WSJ, Barnes joined Facebook’s political ad sales team in 2013 from a digital consulting firm that worked on Sen. John McCain’s presidential campaigns. He became the go-to person for the Trump campaign as part of a team that worked exclusively with Republicans.

His work involved helping the campaign steer fundraising ads to the screens of people who ‚liked‘ Trump’s Facebook’s posts, the Journal reported.

Barnes‘ tools became invaluable to the Trump campaign, which lacked much of the traditional fundraising apparatus including donor databases that an established career politician would have possessed, according to the WSJ.

A few days after Trump’s election upset in 2016, Gary Coby, his campaign’s digital director, reportedly sent out the following now-deleted tweet: „Aggressive learning agenda; multivariate testing w/FB helped us quickly learn path to max $$$ and message. @jameslbarnes of FB was a MVP.“

Although the Trump campaign relished Barnes‘ work, he and other colleagues grew increasingly uncomfortable with Facebook’s political dealings and its involvement with the then-presidential candidate.

Earlier this year, Barnes departed Facebook He is now working at a progressive nonprofit called Acronym to prevent Trump from getting reelected.

In a Facebook post this summer, he reportedly wrote that „Make America Great Again“ was about „activating the deepest, darkest, soul of white nationalism.“

Facebook remains important to Trump’s political career. On Wednesday, the official Twitter account for Team Trump slammed Facebook, saying the company wanted to remove „tools that help us reach more great Americans & lift voices the media & big tech choose to ignore.“ A top Facebook advertising exec Carolyn Everson had said the company was considering options for changing its political ad targeting mechanisms, adding that nothing was off the table.

Facebook has not yet given a timetable or details on the changes it might make to its advertising tools.

Read the full story on The Wall Street Journal.