GOP presidential front-runner Donald TrumpDonald John TrumpDems make history, and other takeaways from Tuesday's primaries Pawlenty loses comeback bid in Minnesota Establishment-backed Vukmir wins Wisconsin GOP Senate primary MORE is mocking former Gov. Martin O'Malley (Md.), a Democratic contender, for apologizing to Black Lives Matter activists.

Trump said O'Malley showed he had no spine following a confrontation with the protest group last month.

“He apologized like a little baby, like a disgusting, little, weak, pathetic baby, and that’s the problem with our country,” Trump told host Jeanine Pirro on Fox News’s “Fox & Friends” Friday morning.

“How can you apologize when you say black lives matter — which is true — white lives matter, which is true — all lives [matter] — which is true?” Trump asked of O’Malley.

“And then they got angry because you said white and all, [but] we don’t want you to mention that,” he added. “What does he need to apologize for?”

O’Malley’s campaign countered that his overtures to the activists show an inclusiveness that Trump’s 2016 platform lacks.

“Governor O’Malley stands with those who have the guts to stand up to Donald Trump’s hate speech,” Lis Smith, O’Malley’s deputy campaign director, told The Hill.

“It speaks volumes about the Republican Party today that this is their frontrunner,” she added of Trump. “Unlike the rest of the Republican field, we’re not interested in engaging in a race to the bottom with Mr. Trump.”

Trump’s jab at O’Malley came the day after the Democrat led a demonstration in Las Vegas for union rights that included Trump International Hotel employees.

The Black Lives Matters protesters have disrupted speeches by O'Malley and Sen. Bernie SandersBernard (Bernie) SandersDems make history, and other takeaways from Tuesday's primaries Ellison wins Minnesota AG primary amid late domestic violence allegations Ironworker and star of viral video wins Dem primary for Speaker Ryan's seat MORE (I-Vt.), another Democratic presidential candidate.

At one event, O'Malley responded to the chants of "black lives matter" by saying that "all lives matter."

The activists argue that response misses the discrimination faced by African-Americans in the judicial system.

O'Malley later apologized, saying that he "meant no disrespect." 

— This story was updated at 12:30 p.m.