Measuring Presidential popularity with merchandise

There are traditional ways to measure Presidential popularity: polls that in some way measure approval or disapproval. Here is another possible way: sales of Presidential merchandise.

I’ve always wondered why Presidents or other political officials allow such merchandizing using their figures and words in order to make money. Perhaps it is simply publicity (even if it is in opposition to them). Or perhaps they don’t want to appear to be the politicians who cracks down on such things. Or perhaps by running for or entering public office, there is a tacit understanding that they are now in the public eye and can be used for money-making purposes.

And what does it mean culturally to reduce any politician to a piece of merchandise?