US companies and the collection of US voters are different. Their interests do not always coincide.
One might say that higher margins are "good for the US economy", but that doesn't mean they're good for every person participating in the US economy -- which is what the US voter cares more about.
It's important to recognize that US Companies, to a great degree, are owned by shareholders. It is the shareholders who receive the profit.
The fact that Walmart sells goods manufactured overseas, giving it higher margins, has allowed various members of the Walton family to become billionaires. But someone working as a Walmart greeter probably sees very little benefit.
And, of course, the now unemployed US manufacturing workers/voters do benefit a little from Walmart's lower prices as customers. But, it's reasonable to question whether such workers are better off unemployed, even if they are able to buy cheap products from Walmart.