The American Family Association's pledge to boycott Target because of its policy to allow men into women's bathrooms, and vice versa, has reached 1.3 million signers, and Target's stock (TGT) continues to suffer compared to that of its natural competitors.

At the close of trading on Tuesday, the boycott-induced direct decline in Target's market cap was $9.2 billion.  By the end of this week, that exceeded $10 billion.

Since April 19, the date the policy came into effect, Target's market cap has declined 19.4%.  By comparison, the corresponding market cap of natural competitors such as Costco (COST), Walmart (WMT), Dollar General (DG), and Dollar Tree (DLTR) has displayed an entirely different behavior over this time frame.

Costco's market cap has declined only slightly (3.0%), whereas Walmart is up 1.4%, and Dollar General and Dollar Tree have both increased 7.6%.

In the period before the boycott began, Target's market cap was most closely correlated with Walmart, making Walmart's post-boycott market cap pattern the best counterfactual for how Target's stock would have performed absent the introduction of the company's controversial bathroom policy.

If Target's stock had continued its pre-boycott correlation with Walmart, the company's market cap would currently be $51.1 billion.  But it is not.  Rather, the present value is just $40.6 billion.

The reasonable conclusion is that the market cap cost of the boycott is now $10.5 billion and still rising.