I’ve heard of it long before Trump. MS-13 is a real thing and they are exceptionally violent as gangs go. It is ironic that they originated in the US and then deported, only to grow larger because of it, and now are framed as some external invasion.
But as serious of a problem as MS-13 is in some areas (I mean, their mottos are variations of "rape, control, kill”), their reach size is pretty small with an estimated 10,000 in the US, which is ~1% of all street gangs. But similar how the Bloods and Crips were the go to face of street crime in the 80s and 90s, MS-13 is now the great boogie man. And that boogie man has been exagerated into an “invasion” pouring through the border.
And that there is the whole bullshit spin on this. Trump acts like the handful of “animals” he says he is trying to protect America from is the majority of refugee and migrants coming over the border, when in reality they are a tiny, tiny percentage (and there are more criminals from other cartels doing actual smuggling than MS-13). This is just like any other time when we have demonized the whole of the other because of a tiny percentage of bad actors. Like when the Germans and Japanese were all assumed to be saboteurs and traitors during WWII. And then because some sane people are rejecting this false premise, then you have memes floating around that Democrats want MS-13 to come in and rape and kill with abandon. It is absurd, but that is what is going on in some peoples’ minds.