More than 20,000 public school teachers in California opened their mailboxes over the last few days to find a pink slip inside as districts dispensed the dreaded news to the educators that they may not have a job in the fall. The layoff notices are preliminary, the districts' best guess at their funding after the Legislature concludes its annual budget fight this summer. But a proposed tax measure on the November ballot offers more uncertainty. Voters could approve a tax increase that would prevent a $4.8 billion trigger cut to education funding, as proposed in the governor's budget. That cut...