2A people are highly motivated to turn out to vote and were a major part of his support.
(I was at a 4 day shotgun class during the election; there were long debates about the two acceptable candidates on multiple issues -- Johnson vs Trump.)
Post-Trump, many progressive people of color are arming themselves out of fear of white nationalists. None of them want a gun ban.
Hillary specifically was pushing for an "assault weapons ban" in multiple speeches, and magazine capacity bans, under the phrase "common-sense gun regulations." Who knows what actually would have come to pass, but she was definitely not going to put pro-2A justices into SCOTUS or expand 2A protections.
It's just very hard for me to understand how this issue (or others like abortion) would be above all others. You are voting for a government with a tremendous amount of power and responsibility (military and defense, infrastructure, running a huge economy, world trade, healthcare, etc). I just can't imagine voting based on a single issue like the 2nd amendment while ignoring all the others.
I respect your opinion, and I know you are not alone. It's just hard for me to understand it, that's all.
[0] I've always wondered what would happen if democrats adopted this into their platform, maybe in exchange for universal background checks.
(I'd be supportive of both some kind of pre-purchase background check AND of some way to trace a physical gun used in a crime to a registered owner provided it also did NOT build a registry of all guns owned by a given owner, or a way to identify that a given person was an owner of guns or not. There are some technical ways to implement this, especially the latter.
There have been technical improvements to NICS over the past few months which have made it both more efficient AND more accurate; there's a lot of potential to improve the existing background checks used for all sales via dealers, and once it gets good enough, it's a lot easier to provide access to it for private party transfers as well. If I were in a state where I could privately sell a gun to someone w/o going through an FFL, I'd be uncomfortable selling to anyone I didn't know personally, and given that I know how hard it is to validate physical credentials well without checking a centralized database, even something like LE ID wouldn't be as comforting as being able to make a NICS check. Outside of known-person transfers, I'd generally rather just spend the $10-25 to let an FFL handle the transfer for me, although this is already legally required in WA state.)
So, whether or not you agree with her, you can see that there is some logic to making that issue a high priority if she views it that way. "Hitler's really got a great economic package, has better public experience than his opponent, is better all across the board, and is in favor of the extermination of a bunch of helpless people."
In my mom's case, she'd be Democrat, except for this one issue. She's pro Syrian refugee, pro immigration, against capital punishment, etc.
I hope she understands that prior to Roe vs Wade, abortion still occurred, and women died in many cases because they didn't have access to a safe clinical means to obtain them.
She should understand that if the laws are changed regarding abortion, that women will still have abortions, will still need abortions, and will still find means to obtain abortions - even if it kills them - which it most assuredly will.
If she is fine with that - if she is fine with women dying - then I don't know what to say.
If she really wanted to decrease the number of abortions, she (and others like her) would do what we know actually works: Increase access to contraceptives, and teach people proper non-abstinence based sexual education.
But we are unlikely to see that really happen - because being anti-abortion isn't about saving the unborn, it's about punishment (via pregnancy and birth) of women for having sex (premarital or otherwise as it happens).
Bill Clinton said it best: abortion should be safe legal and rare.
/yeah, I know such restrictions happened mainly because so many "gun-nuts" just couldn't stop buying, fearful that their guns and ammo were going to be taken away by Obama - I've read blogs of such people who perfectly know this to be the case, yet it continued. Gun store owners and manufacturers smile when a liberal is "in charge", because they know sales will go thru the roof - always does.