A TV crew from Channel 10 news printed a plastic gun, and managed to get it within a few meters of Bibi. The gun was manufactured with a 3-D printer, tested, and brought to Knesset, where it got past all security checks, including a metal detector. That 3-D printers can print a working gun based on plans easily available is not new, but reports of a gun made with the technology bypassing safeguards in a secure building are (do far) rare, AFAIK.
However, there's good reason to not be so alarmed about this.
Firstly, 3-D printing is a way of making something out of a plastic (or plastic-like) material. Such materials are hardly new. In the Clint Eastwood film In the Line of Fire, (spoiler alert; but seriously, the film is 20 years old) John Malkovich's protagonist manages to fire at the president using a gun he made out of plastic. Not only has plastic technology been around for many, many decades (remember the scene in The Graduate where Dustin Hoffman's character is advised to go into plastics?), but the idea of sneaking a plastic gun past security to assassinate a world leader hit the big screen 20 years ago. 3-D printing is not what got the gun past security, plastics did. Somehow, even with plastics easily available, and the idea of using a plastic gun to foil security being well-known for decades, we've haven't seen people successfully sneaking plastic guns into secure buildings and using them there.
Secondly, to misquote the bumper-sticker, guns don't kill people, bullets do. And, so far, they are made out of metal. Getting a gun to within 2 inches of a target won't help a would-be assassin unless he could somehow get the bullets there as well. (In fairness, they covered this in the movie as well, but I don't know how well a movie stratagem would work in real life.) As long as the Knesset still uses metal detectors, and as long as bullets are still made out of metal, I think we could breathe a little easier.
While the fact that a gun was smuggles into the Knesset, and got within firing range of Bibi, is disconcerting, bear in mind that it was done for dramatic effect, and doesn't necessarily mean that things are all of a sudden less safe than they were yesterday.