That decline has been driven by a steep drop in the number of visits by women.
Many of Trump's branded properties are located in states that have frequently voted for Democrats, including New York, New Jersey and Hawaii. Over the past five months, foot traffic at those properties in these states has dropped year over year as a share of the market — according to Foursquare — spurred by a plummeting share of female visitors.
Just this July, visits by women to Trump-branded properties in "blue states," which lean Democratic, were down as a share of the market by 29 percent year over year. Since this March, every month has seen at least a 20 percent decrease in visits by women measured year over year.
In a blog post reporting the broader findings, Foursquare said that it normalized its data against U.S. Census data and that the company looked at "market share" to understand changes over time as compared to "competitive properties in the same area."
The Trump Organization did not respond to a request for comment.