Yes, as I said, you can cherry-pick various trade issues. Heck I can even find long-running trade disputes on certain products -- one that immediately comes to mind is the long-running dispute between Canada and the US over lumber (https://en.wikipedia.org/wiki/Canada%E2%80%93United_States_s...). What's "fair" in these type of disputes of course depends on which side you are on, of course.

I just wasn't aware of any major outstanding issue that required a "trade war" type scenario with these countries (EU/Canada/Mexico) now.

The issue with trade wars is that the tariffs that result can end up lasting far longer than one might expect, and from what I see most economists consider the overall impact negative. The 25 percent tariff on light trucks in the US for instance comes as a direct result of a minor "trade war" between West Germany and France on chickens from approx. 1961-1964. (https://en.wikipedia.org/wiki/Chicken_tax)

Generally speaking, if a tariff another nation imposes is bothersome, removing tariffs in a negotiated deal is what has tended to work over the last several decades. That 10 percent auto tariff was recently negotiated away in Japan, for instance, with Japan likewise removing some tariffs they applied on EU products. (http://europe.autonews.com/article/20171208/ANE/171209797/eu...)

In the case of China, where they are more prone to violating WTO rules, that approach might not work, and a more aggressive stance might be justified. But the EU, Mexico, and Canada? Not so sure there.