What is the message of the cartoon? How can this cartoon be used to answer the mini question?

Note:

As Senate Majority leader, Lyndon Johnson did not directly oppose the 1957 civil rights bill. However, he did
help push through a provision saying that anyone accused of violating the act would get a jury trial. This made
it likely that any defendant in the South would be tried by an all-white jury and acquitted [let go]. Note also the
playful inscription to Johnson by cartoonist Ed Holland.

mini-q question is :

Why Did L B J Sign the Civil Rights Act of 1964?