In Arizona, Gov. Jan Brewer is required by law to set the date of the state’s presidential nominating contest by issuing a proclamation 150 days in advance of the voting. Ms. Brewer is mulling the idea of setting the state’s primary on Jan. 31, and a decision would have to come by this Saturday.

If that happens, Arizona would set off a cascade of other changes in the 2012 voting calendar. As described by my colleague Jeff Zeleny recently, Florida would almost certainly move its primary ahead of Arizona as it seeks to retain the influence over the choice of nominee it had in 2008.

That would, of course, force Iowa, Nevada, New Hampshire and South Carolina to schedule earlier contests so that they can remain at the front of the pack. Longtime political observers believe that voting could start in Iowa as early as the first week of January.