Of all the questions prompted by last week's governmental shutdown, this may be the most persistent, the one that the most Americans, alternately bewildered and horrified by the spectacle in the capital, found utterly confounding: What were they thinking?For the truth is that none of the principals marched unthinkingly into the shutdown showdown. They knew what they were doing, and they had examined the tactics and consequences. This confrontation may have seemed thoughtless, but it was just the opposite.