Donald Trump has been a magnet for publicity, especially during his presidential run. Some companies have even found ways to tie unofficial promotions to him.

But despite the often-claimed strategy that any publicity is good publicity, there's a question of whether that is true. For Donald Trump, the answer is no, according to a new report from online real estate company Redfin.

The report says that since his presidential run, Donald Trump has seen the value of his personal brand drop significantly in the area where it is most important: real estate. Property branded with his name has dropped in value whereas nearby comparative properties haven't.

In the first five months of 2015, the Trump name was associated with a 6.8 percent sales premium compared to similar properties. That differential has disappeared. On a square foot basis, Trump properties sold for 9 percent more than comparable units in 2015. Again, the difference is gone. Now, Trump units were on the market for about 10 days longer than comparable ones last year. This year it's 9 days without the benefit of the additional price. (Time on the market is an issue in real estate because there are always carrying costs in taxes, utilities, and mortgage payments.)

The Trump Organization sent a statement. It said, in part, a "one-bedroom unit at Trump Chicago sold this year at a record breaking price" and that "there is clear evidence that the premium placed on Trump properties is as strong as ever." Of course, mathematically a single sale could set a record for the company and the average premium could still drop to nothing, as Redfin claimed.

In addition, Yahoo Finance claimed to have found modest rate discounts at Trump hotels. The Trump Organization also claimed that "many of the hotels referred to in the article have an [average daily rate] that significantly exceeds our competitive sets," which means the groups of hotels the company picks as direct competitors, not necessarily the hotels that Yahoo Finance chose as competitive.

According to Redfin, the drop may not necessarily be politics. Market conditions might have changed and driven down the cost of "uber-luxurious condos," according to Redfin chief economist Nela Richardson, as quoted on a company blog post. "The luxury market has been fighting a chill since late last year and even the gold-plated faucets in Trump's bathrooms can't overcome a slowdown in demand from wealthy buyers caused by the rocky global markets in 2016."

Still, the juxtaposition shows that even the massive publicity that Trump has gained during this election cycle at best may not overcome market forces and, at worst, could have a negative impact on brand.