Irony is one the best tool caricature artists has in getting a message across. Bill "Whitey" Sanders, who was a caricature artist for 34 years, used irony in his works. Here he has Nixon, identifiable by his nose and brow, Paints graffiti saying "democrats are soft on crime." Nixon would later be put on trial for his political crimes, losing the presidency because of it. So his slogan was incorrect, Democrats did take strong action against criminals, Nixon, and because he is calling for stronger enforcement against crime, and he himself is committing crimes, it is ironic.
The interesting thing is that this is not about Watergate, this refers to a political move of Nixon's, He was trying to appeal to the idea that he had changed, or what was called the "New Nixon," and was depicted with him smiling, opposed to his "mean" look. the man holding the "New Nixon" mask says, "Say, mister, you dropped your mask." The artist is saying a few things here. he is saying that Nixon hasn't changed, that "New Nixon" attitude is fake, and that he is unable to keep up that appearance. So while Nixon presents himself as changed, in truth he hasn't changed at all.