It’s been decades since Democrats had to confront a genuine challenge from the far left. Notwithstanding the unity that President Trump seems to have offered the party in the last few days, recent events show that period of relative unity among Democrats is probably temporary.

The cracks in the party were most evident last week after Rep. Alexandria Ocasio-Cortez (D-N.Y.) casually deployed the race card against House Speaker Nancy Pelosi (D-Calif.). To be sure, Ocasio-Cortez’s side swipe — implying Pelosi singled her and her progressive allies out for criticism because they are women of color — was bad enough. But the real depth of the challenge Democrats face is better seen by looking at comments from Ocasio-Cortez’s chief of staff, Saikat Chakrabarti.

Chakrabarti attracted derisive attention from the House Democrats’ official Twitter account late last month when he said that moderate Democrat Rep. Sharice Davids (Kan.) was “[enabling] a racist system” through her votes. The fact that Davids is a gay Native American did not seem to matter to him. Nor did the political realities she faces. (She flipped a suburban Kansas City seat in 2018 that voted staunchly Republican before Trump.) The only thing that seemingly matters to Chakrabarti is that she hasn’t supported a revolutionary uprooting of the United States’ political and economic systems.

This charge echoes some of the historical fights within the American left. In the early 1920s, communists who believed in revolutionary change of Western democratic capitalism broke with their more moderate Social Democratic colleagues. What had once been a unified international left under the umbrella of the Socialist International became divided with the revolutionary elements grouping under the Comintern. In most Western European nations, the two strands of the left battled politically for decades, with the evolutionary left striving to keep the revolutionary left at bay.

This battle came to the United States after World War II. The Democratic Party’s left wing split from the main body in 1948 because of the former’s opposition to the Soviet Union and unwillingness to impose socialist economic planning. The Progressive Party withered at the polls, attracting only 2.4 percent of the vote. Democratic Party leaders such as George Meany also ensured that labor unions were free of communist influence. By the early 1950s, the far-left threat was over. Evolutionary left-wing politics had won.

Observers may wonder why Ocasio-Cortez and her chief of staff are engaging in this internecine battle. From the viewpoint of the evolutionary left, such efforts are futile and self-defeating. But that assumes Ocasio-Cortez and Chakrabarti share the Democrats’ historic commitment to center-left, evolutionary change.

Chakrabarti let the cat out of the bag in a recent extensive profile in The Post magazine. According to the report, Chakrabarti told an aide for Washington Gov. Jay Inslee (D), a presidential candidate, that his boss’s Green New Deal “wasn’t originally a climate thing at all.” “Do you guys think of it as a climate thing?” Chakrabarti says, “Because we really think of it as a how-do-you-change-the-entire-economy thing.” You can’t get much more revolutionary than that.

It’s no coincidence that the Green New Deal speaks as much about ensuring quality jobs and helping “frontline and vulnerable communities” as it does about reducing greenhouse gas emissions. It also calls for an “economic mobilization on a scale not seen since World War II,” uprooting the U.S. economy with the government calling the shots. It’s what conservatives label “watermelon politics” — green on the outside but deep red on the inside. Its excursions into economic policies and guarantees are a feature, not a bug. Chakrabarti clearly understands this all too well.

If the entire U.S. economy must be uprooted — if the United States is inherently a “racist system” — then those who propose evolutionary change are as culpable as those who oppose any change at all. They must be opposed as strenuously — perhaps more so, since civil wars are always bitter — as the system’s stalwart defenders. And that, my Democratic friends, means you.

That’s why Justice Democrats, the group Chakrabarti helped found, continues to recruit primary challengers to Ocasio-Cortez’s colleagues. It’s nothing personal, mind you. They’re just in the way of the revolution.

The challenge could be ignored if it came only from Ocasio-Cortez and her staff. But they are not alone. Many others who call themselves “democratic socialists” won party primaries in 2018 and now sit in state legislatures. Ocasio-Cortez’s “squad” may only be four votes in the House, as Pelosi said, but they have online followings numbering in the millions. Sen. Bernie Sanders (I-Vt.) mobilized the far left in his 2016 presidential bid, and his fight with fellow Democratic presidential candidate Joe Biden over his Medicare-for-all proposal shows he is not backing down, either. Ocasio-Cortez may be on the far-left flank, but millions of people are not far away.

I disagree with many Democratic policies, but almost all Democrats do not want to rip up the U.S. economy root and branch. Ocasio-Cortez and her chief of staff, however, do. That means Democrats face a decisive choice.

The ideological ancestors of today’s Democrats faced the same choice and passed the test. They stood firm in favor of evolution rather than revolution. They were willing to lose votes on the left and the right to maintain connection with the center. President Harry S. Truman, a Democrat, was written off as a goner when the progressives and the racist Southern Democrats both split from his party to run their own candidates. But Truman kept faith with the American center by letting both extremes walk, and he won one of the greatest political upsets in history.

Democrats should follow Truman and say goodbye to their party’s bomb throwers before it’s too late.

Read more: