I have tried to write about "the Overton Window" before, and... here goes, again.
It is one of those concepts that is intellectually valuable, but difficult for those of us mathematically inclined because it is difficult to specify in mathematical terms. Essentially, there is a range of options that are "conceivable," and that range can expand or contract, or move left or right. Part of politics is moving that window. Something that was once inconceivable can become conceivable, and that changes a political dynamic.
This is most obvious with Trump in terms of his corruption. Really, though, every time Trump opens his mouth or tweets, he redefines what is and isn't conceivable. (Must... not... use... obvious... link...)
So, the arming teachers thing. This isn't going to happen. Make sure you have a coherent argument about this, though. None of this GUNS ARE SCAAAARY stuff. So,
1) Trump wildly overestimates the number of teachers who have even the most basic understanding of how to handle a gun.
2) Trump wildly overestimates the number of teachers who have any willingness to handle a gun.
3) Handling a gun in a crisis requires extensive tactical training.
4) Handling a gun in a crisis is extremely psychologically difficult, and even those few who can hit a target at the range mostly can't do it in a crisis. Estimates vary, but less than half of soldiers in combat actually fire their weapons. Soldiers.
So, even if we grant Trump a "mulligan" on 1 and 2, like the Family Research Council did for all of his affairs, he's just a fucking moron for not understanding 3 and 4.
Note what I'm not doing. I'm not saying, "GUNS ARE SCAAARY!!!!" What I'm doing is called, "logic." I've said it before, and I'll say it again. Guns drop the IQ levels of everyone in American politics.
Anyway, guns in schools? No. Dumb idea, and it won't happen. But, Trump promoting it?
That matters. Why? The Overton Window.
We have a difficult time in this country acknowledging the fact that the President is a batshit crazy moron. Political norms require us to treat policy positions from the President as acceptable, and within the Overton Window, simply because they are promoted by the President, based on the premise that a president cannot, by definition, be a batshit crazy moron. Ideas, then, are normalized to at least some degree simply by having a president say them.
There is a range of positions on any issue that can be considered within the Overton Window. Expanding the Overton Window in either direction expands the realm of possible outcomes in that direction. Ideas outside the Overton Window are generally considered to be batshit crazy. However, if we treat any position the president takes as defined to be not batshit crazy, then the act of the president taking a position puts that position within the Overton Window, and expands the Overton Window in that direction.
Trump advocates giving guns to teachers. It won't happen, and Trump's statements don't make the idea any less batshit crazy. However, the fact that Trump is taking the position, publicly and repeatedly, means that we are expanding the realm of positions that are considered publicly. Ideas less extreme, then, are placed in comparison to the idea of arming teachers. The policy debate shifts to the advantage gun control opponents who take less extreme positions simply because the Overton Window has shifted. Anyone who doesn't advocate giving guns to teachers suddenly looks like a moderate.
Moderation and extremism are relative. This was a common point I had to make during the 2016 Democratic nomination contest because of the damned Bernie people. Any time someone pointed out that Sanders was an extremist within the context of American politics, the response from anyone who had quaffed deeply from the Sanders kool-aid was to say that Sanders wouldn't be considered an extremist in Denmark.
Which would have been relevant if he had been running for office in Denmark.
Moderation and extremism are relative.
Trump is an idiot and not remotely connected to reality. Arming teachers is not going to happen. The fact that Trump is promoting the idea, though, shifts the debate. It shifts the Overton Window, and makes other positions less extreme by comparison.
Note, though, that this wouldn't happen if we treated Trump the way we should: like the batshit crazy moron he is, whose every word should be ridiculed. Our political system still cannot fully adjust to the fact that our President is not mentally or psychologically fit for office.