Get this: For some on the left, even the ultra-radical Netroots crowd isn’t crazy-extreme enough.

Democrats learned that the hard way last weekend at the annual Netroots Nation, a gathering of tech-savvy “progressives.”

Two presidential wannabes, former Maryland Gov. Martin O’Malley and Vermont Sen. Bernie Sanders, were interrupted by “Black Lives Matter” protesters at the event. The activists commandeered the stage and demanded that both men address police-brutality issues and pledge to “dismantle structural racism.”

The candidates, of course, were aiming to please. Yet O’Malley accidentally committed a cardinal sin: He asserted that “all lives matter.”

Uh-oh: That was just too much for the leftist wackos. They booed and hissed, and claimed his comment distracted from the BLM message.

Worse, O’Malley then caved to the extremists and apologized. Sanders, meanwhile, couldn’t figure out exactly what the protesters wanted. Eventually, the 73-year-old socialist — who marched with Martin Luther King, Jr. — walked off the stage.

Again, Netroots attracts the far left wing of the Democrats’ leftists. But if wannabes like O’Malley are going to suck up to them, it’s fair to wonder if the radicals will drag the whole party into the fever swamps.

True, Democratic front-runner Hillary Clinton skipped the Netroots shindig. Wise move, it turns out.

But as primary season heats up, will she stand up to the radicals — or cave like O’Malley?