Analysis
Perhaps the people most affected by the Zimmermann Telegram were average Americans. While the careers of politicians and bureaucrats were made or ruined because of this little note, ordinary Americans died because it dragged their country into a war they didn't want to be in. The U.S. drafted men to fight in World War I, meaning that some didn't have much of a choice when it came to packing up, sailing to Europe, and shooting at Germans.
None of which might have happened without the Zimmermann Telegram.
Before 1917, the American public did not want to go to war. And even if they did get involved, it wasn't a sure thing that they would be on the side of the Allied Powers. There were some who sympathized more with Germany, or at least weren't sold on helping the British.
If you'd conducted a survey of Americans before the Zimmermann Telegram was made public, a majority would have told you that they were pro-neutrality, and all for making money off the war. The consensus was that it was perfectly legitimate for the U.S. to sell stuff (mainly to Britain because they paid well) and still be neutral. Women, many of whom were actually voting these days, were especially vocal about not wanting to send their sons and husbands off to die. Immigrants from all over the world hoped that the U.S. would, unlike their former homelands, not make them fight in pointless conflicts.
Don't Mess With Texas (or Arizona or New Mexico)
But of course the Zimmermann Telegram changed all that. Okay, American ships being sunk by German U-boats helped, too, because it made the war less profitable for Americans, but it's all part of the same basic issue, which was Germany's aggression.
The American view of "Germans or Brits, what's the difference? It's not our war" evaporated in just a few months, when the Zimmermann Telegram was released and unrestricted submarine warfare was resumed. Americans started hating everything German. This blind range toward a new enemy took forms that were harmful and others that were just silly. There were German-Americans imprisoned and harassed in cruel xenophobic ways. There were also people who started calling sauerkraut "liberty cabbage" and hamburgers "Salisbury Steaks," as if that mattered. (We're looking at you, "Freedom Fries.")
It's unsettling how quickly public opinion can turn on an issue. One day nobody cares about the goings on across an ocean and the next day people are pretending that their dachshunds are "liberty dogs" and that only the bad kids study German in school. The mind is a strange and unreasonable place, capable of being triggered by even something as small as a one-paragraph telegram that wasn't even addressed to them.