When the cast and crew finished the cold read (first read-through of the script), a producer told them that a restaurant in Israel had been attacked by a suicide bomber with 15 civilians killed--including an American citizen. The cast was stunned not only by the tragedy but how closely it mirrored the events of the script, with Richard Schiff calling the news "mind-blowing."
This episode's title refers to the day before Yom Kippur, which is Erev Yom Kippur. Yom Kippur, "Day of Atonement", is the holiest day of the year in Judaism. Jews traditionally observe this holy day with a day-long fast, confession, and intensive prayer, often spending most of the day in synagogue services. The name Yom Kippur is based on the Torah verse, "...but on the 10th day of the seventh month it is the day of kippurim unto you..." (Leviticus 23:27). The object is to gain atonement from God. Erev Yom Kippur (lit. "eve [of] day [of] atonement"), on the other hand, is the day preceding Yom Kippur, corresponding to the ninth day of the Hebrew month of Tishrei. This day is commemorated with additional morning prayers, asking others -and not God- for forgiveness, giving charity, performing the kapparot ritual, an extended afternoon prayer service, and two festive meals.
In a reference to the Palestinian leadership, Chairman of the Palestine Liberation Organization Yasser Arafat is mentioned by name. Even though foreign dignitaries were normally fictional on the show, producer Aaron Sorkin said it felt right to call the Chairman by his real name "'cause Arafat's been around forever and he'll be around forever". In a later episode, however ("Gaza" in season five), the name of the Chairman of the Palestinian Authority was changed to Nizar Farad, a fictional character. By that point in mid-2004, Arafat was in failing health in real life, and would die in November 2004. The show continued to use the Farad character and never made any references to Arafat's successor Mahmoud Abbas.
The West Wing episodes were written close to production and at the time of the September 11 attacks Aaron Sorkin was writing on episode six of the season ("Gone Quiet"), which originally was to air on Halloween (October 31). The events caused consternation in the writing staff, and the episode had to be entirely rewritten. "I was kind of paralyzed," said Sorkin, "I didn't know what to write". Because of the attacks, air dates were postponed and the already finished "On the Day Before" became the Halloween episode instead. Nevertheless, the episode took on greater relevance to actual, international events than the writers had intended. On August 9, after the actors had just done a cold reading of the episode, they were informed about the Sbarro restaurant suicide bombing, a Jerusalem suicide bombing in which an American was killed. The close similarity to an event in the script came as a shock to the actors.
CJ (Allison Janney) says this is the President (Martin Sheen)'s first veto - however on episode 4 of season 2 on Capitol Beat (where Ainsley Hayes (Emily Procter) is introduced) the presenter says that the President veto'd a Republican education bill the year before.