Reuters: CARACAS - Drones loaded with explosives detonated close to a military event where Venezuelan President Nicolas Maduro was giving a speech on Saturday, but he and top government officials alongside him escaped unharmed from what Information Minister Jorge Rodriguez called an “attack” targeting the leftist leader. Seven National Guard soldiers were injured, Rodriguez added.See this 2015 post on drone racing and ask yourself how you'd stop one of these drones from getting close to its target.
Countermeasures will be quite difficult, especially if drone operators use sophisticated frequency hopping control.
One doesn't even need pilot operators. The drones can be programmed to fly to a GPS coordinate using an evasive approach.
1. The exact coordinate can be marked by someone in the audience of a public appearance of the target.
2. It would be a formidable challenge even to stop some medium sized drones, each with a few kilo payload, from flying through the windows of the Oval Office (known GPS coordinate; known presence of targets at specific times).
This is still Science Fiction, for now:
Twenty years ago I told a PhD student that a terrorist -- willing to die and able to fly an airplane -- could probably take out the White House. After 9/11 he reminded me that I had identified this hole in the system well in advance. It's the same thing here with small and medium size drones. They are accessible to non-state actors with limited resources, and very difficult to defeat, even for state security.