Because Canada has been in trade talks with China and may potentially lower its tariffs on China which gives them a back door into the US. There are some specifics and it's all conditional. It depends on the kinds of deals it settles on.
It's not a back door to anything. It's competition for the US and Japanese automotive manufacturers who are protected by the existing tariffs.
It's not a back door to anything. It's competition for the US and Japanese automotive manufacturers who are protected by the existing tariffs.