That's the thing about executive orders. Trump can make case-by-case exceptions for things like trainloads of auto parts.
Make the globalists feel the pain.
Quite right. However, U.S. economists and university professors are all over the news this morning declaring that a border closing would be "insane", "unbelievable" "shocking", "cataclysmic". etc.
That blatantly anti-Trump, anti-American message will saturate the news as the possibility of a closure nears. Team Trump will need to respond effectively and that will require the full support of R politicians.
Those who advocate impeachment will be closely watching and measuring any loss of Trump R support, along with the usual encouraging of those who might be tempted to abandon him.