So he's using steel tariffs as leverage

We now have a better idea of Trump's end game on steel tariffs.

US NAFTA trade negotiator said Canada and Mexico will get an exclusion from US steel and aluminum tariffs if they sign a new NAFTA agreement.

So the steel and aluminum tariffs aren't about national security or protecting steel workers or any of the rhetoric; they're leverage, at least as far as Canada and Mexico are concerned.

So Trump and Lighthizer have shown Canada and Mexico what they want, and what will happen if they balk. Lighthizer said he's made more headway with Mexico than Canada.

The next question is: What does Trump want on NAFTA? Some information has spilled out but it's unclear if what the US wants, Canada will agree to. We know that one big hang up is arbitration and that's an area Canada doesn't want to give up ground but perhaps they relent here and hope it's solved if/when the US joins TPP?

Alternatively, Canada can band together with other nations who have been affected by the tariffs and hold the line and punt until after the Mexican election.