Donald Trump's primary target in the hours since the Democratic debate ended: Bernie Sanders.

Trump repeatedly criticized the senator from Vermont on Wednesday, saying Sanders should have aggressively gone after Hillary Rodham Clinton and releasing a video on Instagram that highlights Sanders being overpowered by Black Lives Matter activists.

"The world is a dangerous place," the video narrator says, as CNN video footage of Islamic State fighters plays. "We need a tough, strong leader."

The video then jolts to video footage of Sanders looking confused on a stage at a campaign event as Black Lives Matter activists interrupt him, take the microphone and share their message.

"And it's not this guy," the narrator says, as carnival music plays. The brief video ends with this message on a black screen: “Bernie can’t even defend his microphone. How will he defend the country?”

In sharing the video on various social media platforms, Trump wrote: "We need a strong leader- and fast!"

Republican presidential candidate Donald Trump posts a video to Instagram attacking Democratic candidate Bernie Sanders. (Donald Trump/Instagram)