I’m pretty sure that could be considered grounds for driving up to the Canadian border and requesting asylum as a politically-persecuted refugee

I'd think the same, though it sounds like the US border guards might try to stop him ever reaching the Canadian side. Still, no airline is involved and it doesn't need to be booked in advance so there'd be a pretty good chance of getting through.

I’d think the same, though it sounds like the US border guards might try to stop him ever reaching the Canadian side.

Right now there are only a handful of border crossings from the US to Canada that have border guards challenging Americans leaving the USA, and all of these are new under trump in the last 6 months. The usual place USA border guards challenge is on entering the USA.

Having driven across the US/Canada border multiple times, egress from the US isn’t controlled - or at least, it wasn’t when I went through last time. But I’m also a US Citizen and may not have been subjected to the customs queues in ways that non-US passport holders are - idk, it was a few years ago.

or at least, it wasn’t when I went through last time. But I’m also a US Citizen and may not have been subjected to the customs queues in ways that non-US passport holders are - idk, it was a few years ago.

trump changed this in the last 6 months or so. While there are still many Canadian crossings that you can leave the USA freely (to go to Canadian border guards side), trump has now set up USA border guards on the USA side even for US Citizens attempting to leave the USA to go to Canada. I think there are 6 or 8 right now at some of the largest crossings. Its already announced more are coming. trump doesn't want us leaving.

Any recent sources on this? I found some articles from May of this year. Is it still ongoing? Has it gotten worse?

No recent sources. Months ago the article I read said that this was only happening at 6 border crossings, but there were plans to expand it to more.