US President Donald Trump briefly left the hospital in his car to wave to supporters gathered outside. Trump is being treated for Covid-19 at Walter Reed National Military Medical Centre. The president's visit came shortly after he promised his supporters 'a surprise' in a video posted a video on Twitter. In the video Trump said, “I also think we are going to pay a little surprise to some of the great patriots that we have out on the street and they have been out there for a long time and they have got Trump flags and they love our country. I'm not telling anybody but you, but I'm about to make a little surprise visit.” He added, “I learned a lot about Covid. I learned it by really going to school. This is the real school. This isn't the let's read the books school. And I get it, and I understand it. And it's a very interesting thing.” Watch the full video for more details.