Canada

We already know what the other hypothetical loopholes are. None of them would offer him as much freedom to implement tariffs as the one he's currently trying to use. That's why he's using it in the first place.

As for ignoring the courts, I think it's really important to understand that:

1. Trump hasn't actually followed through on that threat any of the times he's made it so far... They've dragged their heels on a lot of things, but they've never actually managed to fully defy a court order yet. That's why Abrego Garcia isn't in El Salvador. If the Trump admin were actually confident they had the ability to flat out ignore the courts, that guy would still be rotting in Bukele's black site.

2. This is very, very different from ordering ICE to bully immigrants. The Trump admin continuing to enforce a tariff that the courts had struck down would immediately crash the US bond market. Remember when bonds got a little "yippy" and Trump chickened the fuck out? This would be a thousand times worse. Because any tariffs collected by the admin would, eventually, have to be paid back once the rule of law prevails. Yes, I can already see you gearing up to say that the rule of law will never prevail, there won't a 2028 election, etc, etc. I know all that, but international bond markets don't. They are hidebound stuffy old institutions fully of neoliberals who expect norms and rule of law to prevail. Which means that the US putting itself in a situation where it will be forced to repay potentially trillions of dollars in illegally collected taxes (depending on how long the tariffs are illegally enforced for) will look an awful like a serious likelihood of a country going bankrupt or defaulting on its debts. That's the sort of thing that sends bond markets spiralling. Liz Truss collapsed the UK bond market and her own prime ministership by doing far, far less.

It's the second one.

The checks and gentlemen's agreements that the US government is based on don't mean shit as Trump has proven.