As progressives continue to challenge the Democratic Party’s moderate members, former President Barack Obama says he fears that some may be going a step too far.

During an Obama Foundation town hall in Berlin on Saturday, he warned that without compromise, the conflicting ideologies could spur infighting among the left.

“One of the things I do worry about sometimes among progressives in the United States ... is a certain kind of rigidity where we say, ‘I’m sorry, this is how it’s going to be,’ and then we start sometimes creating what’s called a circular firing squad where you start shooting at your allies because one of them is straying from purity on the issues, and when that happens, typically the overall effort and movement weakens,” he told the audience.

Obama recalled his days breaking into the political arena as a young community organizer, admitting that he, too, “wanted change now and I wanted 100% of what I wanted,” only to be disappointed by officials who couldn’t make it all happen at once.

His reaction, he said, was one of furor and frustration.

“I’ve been on both sides of the equation,” he added, emphasizing that principles matter, but so does effective negotiation.

“I think whether you are speaking as a citizen or as a political leader or as an organizer ... you have to recognize that the way we structure democracy requires you to take into account people who don’t agree with you, and that by definition means you’re not going to get 100% of what you want.”

Progressives have gotten more mainstream attention since the midterm elections in 2018, with Rep. Alexandria Ocasio-Cortez (D-N.Y.) quickly becoming one of the movement’s newest and most recognized faces.

She was joined in Congress by the elections of fellow progressive Reps. Deb Haaland (N.M.), Ilhan Omar (Minn.), Ayanna Pressley (Mass.) and Rashida Tlaib (Mich.).

Ahead of 2020, candidates including Sens. Elizabeth Warren (D-Mass.) and Bernie Sanders (I-Vt.) have sought to champion progressive policies such as “Medicare for All” and the Green New Deal, meant to address urgent problems like climate change and skyrocketing health care costs.

Even former Vice President Joe Biden, who is expected to announce a presidential run at any moment, declared himself the most progressive of the dozen-plus Democrats jockeying for the Oval Office.