Ignoring the hypocrisy of Trump's statement for a moment (after all, the political right has also been known to use boycotts as well)...
Does anyone think this might actually backfire on Trump and Marcus?
After all, not everyone knew about the calls for a boycott of home depot, or its founder's support for Stubby McBonespurs. (Before today I didn't.) But now that Trump has tweeted about it, millions of people now know about the situation. (I know I for one will avoid shopping there in the near future, spending my money at Walmart or Rona, and its all because Trump let me know that one of its major shareholders is benefiting from money that is spent there.)
Why is he labeling then "so called" followers?
People don't shop at Home Depot just for the fun of spending money... they do so because they need something. If instead they shop at WalMart or Rona, the money they were going to spend does not disappear... workers still get hired and paid, profits still get earned. Its just a different set of workers and shareholders that benefit.