As with most things in US politics which seem incomprehensible, you need to follow the money to make sense of it. In the 2016 election cycle alone, it is estimated that the NRA and its affiliates spent more than 30 million dollars in campaign contributions to the Trump campaign alone. Of course Trump isn’t going to even hint at suggesting anything which in anyway is harmful to the gun industry.
The same pattern is clear for a large portion of Republican elected officials. The NRA and its affiliates spent an additional 24 million dollars to congressmen, and the vast majority to Republicans. Therefore, regardless of the FACT that there have been at least 8 school shootings in the less than two months of 2018, and more than a mass shooting a day in the same time period - there is zero interest politically to actually change something. Politicians serve their donors, and the NRA owns the Republicans.
As for arming teachers. I’ve worked in education for more than 20 years. Regardless of that, I also remember going to school myself, as most people would. Does anyone NOT have a recollection of at least one incidence when a class/group of kids in a class decided they were going to do their utmost to provoke a teacher as much as they possibly could? Yeah, arming that person is not a great idea!