WordPress HTML editor panel is not showing HTML elements

You can switch back and forth between the editors as much as you want. But the <p></p> tags usually don’t show up in the HTML edit view unless there’s special styling applied to the paragraph (i.e. font size, color, alignment).

Let’s say you have the following in the HTML editor:

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Quisque quis neque sed ligula iaculis
blandit quis et tellus. Aenean et dolor et augue rutrum scelerisque id a orci. Duis odio 
lectus, commodo vitae eleifend a, iaculis id nisl. 

Nunc placerat purus quis nisi vehicula id tincidunt tortor congue. Cras porttitor tortor 
eu arcu faucibus hendrerit porttitor nunc aliquet. Nulla sodales venenatis nisl, id tempus 
est ultrices in. In cursus velit quis ante posuere pellentesque. Aenean feugiat mattis 
adipiscing. Suspendisse ut felis eget neque commodo pulvinar at lobortis ante. Aliquam erat 
volutpat.

There are no <p></p> tags, but WordPress will automatically add them when it passes your post content through the wp_autop filter.

If you want, you can manually add them in the HTML view, but you don’t need to. The extra line break between the two paragraphs is sufficient to trigger a break in the actual markup.