This political cartoon is illustrating the "domino theory", a term coined by Dwight Eisenhower. The Vietcongs goal was to spread communism and the U.S. feared that if they spread it to a certain point, then all of the other surrounding countries would follow suit and eventually spread even farther. This is why the U.S. solider is trying to hold up the other end of the dominoes while Vietnam is trying to push it down.
This is a political cartoon that shows the president Lyndon B Johnson putting himself through a grinder and showing the "peace out" sign. The cartoon is referring to Johnson's pulling out of Vietnam and also out of the presidential race. He pretty much quit altogether.
This political cartoon is making fun of and criticizing the way that leaders are so eager and careless about "setting up troops" over and over again. Just like bowling pins, whenever you need to play again, you set them up just to knock them over.