COLUMBIA, S.C. (AP) — Donald Trump is known for leveling constant and often personal attacks on top rivals such as Joe Biden. Lately, he’s increasingly taking that same approach against independent presidential candidate Robert F. Kennedy Jr.

Among the recent jabs, Trump this past week posted a roughly four-minute video online in which he called Kennedy “fake,” a “Democrat ‘Plant’” and “Radical Left Liberal who’s been put in place” to help the Democratic president. Trump railed against Kennedy’s family as “a bunch of lunatics.”

“He is not a Republican so don’t think you’re going to vote for him and feel good,” the former president and presumptive Republican nominee told supporters in the Truth Social post.

Directing such fierce attacks at Kennedy may signal concern from Trump and his campaign about the independent’s bid in what’s expected to be a tight November election, when a third-party hopeful siphoning even a small amount of support could sink one of the major candidates.