The demonstrators, from the People's Popular Assembly of Oaxaca (APPO), are calling -- among other things -- for the resignation of Gov. Ulises Ruiz, and their protest, which started out in May as an annual teachers' strike, has grown increasingly violent and widespread of late. By late Sunday, police were advancing on a group in the central plaza who were slowing their advance by burning tires and trash and, occasionally, throwing rocks.

The political action is intensifying at a key moment -- for both talks aimed at ending the standoff and the upcoming presidential transition.

On one level, the growing tensions point to the division between the teachers groups that initially took up demonstrations and the separate radical groups that attached themselves to the teachers' cause, uniting as APPO, in June. Both groups have favored calls for Ruiz's resignation, but beyond that they had little in common: The teachers demanded education reforms, while APPO's cause is, at its root, anti-government. With so little to bind them, then, it is hardly surprising that they splintered after entering into negotiations with the federal government. On Oct. 27, the teachers agreed to a deal that would allow classes to resume Oct. 30 -- and made no mention of Ruiz's resignation, a point to which APPO is holding firm.

In recent days, the protests have taken on a more serious tone. At least four people, including an American journalist, were killed when shots were fired in Oaxaca during the weekend, and demonstrations have been taken up in Mexico City as well. In fact, APPO members in the capital on Sunday surrounded a hotel where Ruiz allegedly was staying, demanding to see the guest list -- to prove he was not there -- before dispersing.

Given the rising violence and the break between APPO and the teachers' groups, it appears that President Vicente Fox has had enough. Fox has been notoriously hesitant to use federal security forces in the Oaxaca situation, though the option has been on the table for weeks. The military began conducting flyovers of Oaxaca City on Oct. 1 -- a show of force that temporarily quieted the unrest -- while soldiers assembled in a nearby city. But with supporters outside Oaxaca state taking up APPO's political cause and the clock ticking down toward President-elect Felipe Calderon's swearing-in ceremony, the government cannot afford to let the situation fester any longer.

A negotiated truce between the APPO and police is unlikely: The protest movement has been a rag-tag coalition since its inception, and the poorly organized leadership at this point is having trouble getting supporters to comply even with requests to stop throwing rocks. The stage seems set for more violence. That said, given historical aversions to using federal police to resolve domestic matters, it seems unlikely that government troops will resort to lethal force to quell the unrest.

Fox is attempting to make good on his promise to resolve the crisis before his term ends, but the operation likely has only just begun.