How we cite our quotes: (Paragraph)
Quote #1
Whereas naval units of the Communist regime in Vietnam […] have deliberately and repeatedly attacked United States naval vessels […] (2)
Some pretty clear finger-pointing here. Congress could have simply put "North Vietnam has attacked our ships" and it would still anger Americans, yet they throw in "communist regime." Why? To play on Americans' fear.
Communism was a dirty word during the Cold War, and America was under the spell of a very strong sense of "us and them." (Hint: "them" was any communist nation.) Notice the use of "regime" as well, suggesting a powerful, evil dictatorship.
Quote #2
Whereas these attackers are part of a deliberate and systematic campaign of aggression that the Communist regime in North Vietnam has been waging against its neighbors […] (3)
Again, throwing in "communist regime" as well as "campaign of aggression" really drives home the point that North Vietnam is the clear enemy. Tonkin Gulf Resolution wasn't necessarily meant for the American public to hear, like a speech might, but Congress still needed to be convincing. They can't write a legal document saying "okay, we're off to war!" without any sort of justification. In this case, the justification is clear—America is battling communism, because it's the enemy.
Quote #3
Whereas the United States is assisting the peoples of southeast Asia to protest their freedom […] (4)
Here Congress taps into a sense of values and democracy. By implying that North Vietnam was taking away people's freedom, Congress was sure to get Americans on their side. America is a nation born from the right to protest and be free of tyranny, so it's a safe move to use language like this in a war resolution. Most importantly, this quote suggests that America is the good guy, coming to help smaller countries that only want to be free (whether that's true or not).