WASHINGTON — The Senate today blocked a measure that would have created a path to citizenship for an estimated 500,000 farmworkers and their families, dealing a setback to those who advocate legalization as the key to immigration reform. The measure's supporters failed to secure the 60 votes needed to prevent a filibuster by opponents, ending the effort by Sen. Larry Craig (R-Idaho) to attach the plan to an $80-billion emergency funding bill that mainly would pay for military operations in Iraq and Afghanistan. Under the plan, any illegal farmworker who could demonstrate that he or she had worked in agriculture...