"Being president is like being a jackass in a hailstorm. There's nothing to do but to stand there and take it"

Lyndon B. Johnson is expressing how being president can be a challenging and difficult role. The contrast to a jackass in a hailstorm indicates that the president is constantly bombarded with criticism and difficulties, and they should withstand it without being able to do much about it. Essentially, he is stating that being president requires a thick skin and a capability to handle difficult situations without getting too worked up.