Teddy Goff, Precision Strategies Founding Partner and Obama’s Digital Director in 2012, says “it’s a fairly significant shift.”

Barack Obama’s reelection campaign pioneered a pathway for political campaigns to reach voters through Facebook when it released an app that helped supporters target their friends with Obama-related material.

But as the 2016 presidential campaign approaches, Facebook is rolling out a change that will prevent future campaigns from doing this, closing the door on one of the most sophisticated social targeting efforts ever undertaken.

“It’s a fairly significant shift,” said Teddy Goff, who was Obama’s digital director in 2012, and oversaw the effort that helped the Obama campaign gain a Facebook following of 45 million users that year. Goff’s team used Facebook and other tools to register more than a million voters online and to raise $690 million online in 2011 and 2012.

“The thing we did that will be most affected — by which I mean rendered impossible — by the changes they’re making is the targeted sharing tool,” Goff said.