Former President Barack Obama took aim at his own party over the weekend, sounding warning sirens over the Democratic Party's race to the far-left.

What did Obama say?

During an Obama Foundation town hall in Berlin Saturday, Obama warned that 2020 Democratic presidential candidates are forming a "circular firing squad" that targets one another for ideological "purity" on progressive and far-left policies.

"One of the things I do worry about sometimes among progressives in the United States — maybe it's true here as well — is a certain kind of rigidity where we say, 'Uh, 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 has strayed from purity on the issues," Obama said, according to The Hill. "And when that happens, typically the overall effort and movement weakens."

"So 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 percent of what you want," he added.

Obama warned such stagnate thinking could force many Democrats to compromise their principles.

"You should take some time to think in your own mind and continually refine and reflect, 'What are my core principles?' Because the danger is if you don't know what your principles are, that's when you compromise your principles away," he said.

More than one dozen Democrats — including the likes of Sens. Bernie Sanders (I-Vt.), Kamala Harris (Calif.), Elizabeth Warren (Mass.), and former Rep. Beto O'Rourke (Texas) — have already announced their 2020 campaigns for the White House. More than a half dozen others, including former Vice President Joe Biden, have also expressed interest in joining the race.

So far, candidates have expressed support for a wide-range of once-fringe policies, such as socialist-style health care, free college tuition, reparations for slavery and segregation, and even the controversial "Green New Deal," which is estimated to cost taxpayers $93 trillion.

Anything else?

While in Germany, Obama also met privately with German Chancellor Angela Merkel, the New York Post reported.