Donald Trump wore a hat you can buy on his 2020 campaign website during his recent trip to Texas, and the Internet is up in arms about the perceived indiscretion.

Mr Trump gave a speech during his trip to reassure victims of tropical storm Harvey that all would be okay, and that the government was going to help them. But, some corners of the Internet seemed more interested in the $40 hat on top of his noggin, and accused him of capitalising on a natural disaster to add to his campaign war chest.

“Shame on @realDonaldTrump for using the presidency & #HurricaneHarvey as a platform to make himself wealthier,” one Twitter user wrote, using the President’s Twitter handle to refer to him.

Constitutional scholar Laurence Tribe got in on the action as well, tweeting a Latin phrase - used frequently in law - that basically argues that anyone who has the sole control over something that results in injury can be presumed to be negligent, even if negligence can't be proven.

"The hat Trump wore to his Hurricane Harvey photo-op is for sale on his website," Mr Tribe wrote. "Res ipsa loquitur."

The President was wearing a red cap with “USA” embroidered on the front, while first lady Melania Trump was wearing a cap with the word “FLOTUS” on the front. The hat worn by Mr Trump can be purchased on his campaign website, and has apparently been available there since at least his election since the description on the site still refers to him as a “president-elect”.

The aftermath of Hurricane Harvey Show all 19 1 /19 The aftermath of Hurricane Harvey The aftermath of Hurricane Harvey A tattered U.S. flag damaged in Hurricane Harvey, flies in Conroe, Texas Reuters The aftermath of Hurricane Harvey Lisa Rehr holds her four-year old son Maximus, after they lost their home to Hurricane Harvey, as they await to be evacuated with their belongings from Rockport, Texas Reuters The aftermath of Hurricane Harvey People line up for food as others rest at the George R. Brown Convention Center AP Photo/LM Otero The aftermath of Hurricane Harvey Volunteers with The American Red Cross register evacuees at the George R. Brown Convention Center Reuters/Nick Oxford The aftermath of Hurricane Harvey Soldiers with the Texas Army National Guard help the residents of Cyprus Creek Reuters The aftermath of Hurricane Harvey Residents wade through floodwater Reuters/Nick Oxford The aftermath of Hurricane Harvey Residents walk along the flooded roadway of Texas 249 as they evacuate their adjacent neighborhoods EPA The aftermath of Hurricane Harvey A man floats past a truck submerged on a freeway flooded by Tropical Storm Harvey on Sunday AP The aftermath of Hurricane Harvey People are rescued by airboat as they evacuate from flood waters from Hurricane Harvey in Dickinson, Texas Reuters The aftermath of Hurricane Harvey James Archiable carries his bike through the flooded intersection at Taylor and Usenet near downtown Houston, Texas EPA The aftermath of Hurricane Harvey A massive sinkhole opened up on a motorway in Rosenburg, a city 25 miles southwest of Houston, Texas Rosenberg Police The aftermath of Hurricane Harvey People are rescued from flood waters from Hurricane Harvey in an armored police mine-resistant ambush protected vehicle in Dickinson, Texas Reuters The aftermath of Hurricane Harvey People are rescued from flood waters from Hurricane Harvey on a boat in Dickinson, Texas Reuters The aftermath of Hurricane Harvey Evacuees are airlifted in a US Coast Guard helicopter after flooding due to Hurricane Harvey inundated neighborhoods in Houston, Texas Reuters The aftermath of Hurricane Harvey Evacuees leave a US Coast Guard helicopter after being rescued from flooding due to Hurricane Harvey in Houston, Texas Reuters The aftermath of Hurricane Harvey Residents look on at a submerged motorway during a break in the rain in Houston, Texas EPA The aftermath of Hurricane Harvey People photograph the submerged motorway interchange EPA The aftermath of Hurricane Harvey Debris lies on the ground after a building was destroyed by Hurricane Harvey in Aransas Pass, Texas AP The aftermath of Hurricane Harvey Dominic Dominguez searches for his boat in a boat storage facility that was heavily damaged by Hurricane Harvey near Rockport, Texas EPA

Morality aside, it seems unlikely that the President was doing anything illegal in donning his newest signature cap. While the the Office of Government Ethics, which is in charge of monitoring conflicts of interest in the executive branch, says that endorsements are not allowed, a president or president-elect is exempt from that rule. Plus, he didn’t really “endorse” anything — even himself, or his campaign — since he was just wearing a hat.

It’s not the first time that Mr Trump or his family has been accused of using their high profile to market their products. During the Republican National Convention last year, Ivanka Trump wore a dress from her fashion line, and was similarly criticised. Mr Trump has also hosted campaign events at hotels he owns.

But, the same hat — if not a similar one — that Mr Trump wore to Texas is also available from other retailers. For instance, Walmart lists the hat on its website for a quarter of the price.