But what can you say for one of the highest US houses of governance voting down measures to deny possession of guns to officially suspected terrorists?
Not quite - what the Senate did was not allow the government to deny a federally protected constitutional right without due process of law. Like it or not even suspected terrorists are considered innocent until proven guilty.
When a $500 3D printer can make a usable AR-type rifle from a set of plans anyone can download from the 'net, all the laws in the world won't stop a determined killer. I'm sure we can make it more difficult for criminals and terrorists to obtain firearms without infringing on the rights of the law-abiding. But it's a fool's errand to even think that someone who's set on murder, mass or otherwise, will be stopped because the clerk in a gunshop says "we can't sell you a gun today."