The cliche: Q: What is the best way to criticize your opponent's opinion on taxes? A: Call it a catechism! See, for instance, George Will's column in today's Washington Post. "By accepting, as he had no choice but to do, Congress’s resolution of the crisis, Obama annoyed liberals. They indict him for apostasy from their one-word catechism, 'More!'" See also Andrew Leonard in Salon: "A Republican Party that has made lower taxes the holiest part of its catechism may decide to resist any renewal [of the gas tax] on principle, or at least hold renewal hostage in exchange for other energy-related policy goals." Or Frank Bruni's column in The New York Times: "As [Norquist] walked in and sat down he was sermonizing. As he got up and left an hour later he was still going strong. He seems to live his whole life in midsentence and takes few detectable breaths, his zeal boundless and his catechism changeless."
Where it's from: Catechism, from the Greek for "to sound down," is a religious method of instruction dating to the early Christian church. It is meant to instruct believers on religious doctrine. It can take a question answer format and is often memorized (especially among the illiterate believers of the early church). The Catholic church as well as many Protestant sects have an official catechism. The method of instruction has been borrowed for secular, and especially political, purposes. An actual tax catechism was published and popularized in the 1910s by Charles Bowdoin Fillebrown, a reformist who advocated a single tax policy.
Why it's catching on: Unlike when Fillebrown promoted it in the 1910s, obeying a catechism on tax policy seems to be a very, very bad thing, if we attend to modern usage. The conservative George Will uses it to describe Democratic gluttony, Frank Bruni uses it to criticize Grover Norquist, and Andrew Leonard writes of Republican catechism with a notable sense of doom. Notably, everyone is using it as a pejorative. They mean to imply that people are being inflexible, following a pre-memorized doctrine with the zeal of the (illiterate?) faithful. This doctrine was dictated to them by a higher authority (the party), and this intransigence is why the debt debate became so entrenched in the past month.
Why else? Catechisms have been used in non-religious contexts before, so one might doubt that this is exactly where the metaphor is headed. But the surrounding language -- "apostasy", "holy", "sermonizing" -- makes clear everyone's intention to use a religious metaphor. In fact, their words fit in with a larger attempt in the media to expand the debate to religious proportions. (Anyone hungry for a Satan Sandwich?) It seems the commentators see in the debt debate the same fundamental questions posed by organized religion. Who is right and who is wrong? Whose policy is good and whose is evil? And once that's settled, how to we keep our flock of believers (or congressmen) in line?