In a news conference on Tuesday aimed at pressuring swing-vote senators, leaders of the National Farmers Union, which represents about 250,000 farm and ranch families, stressed the importance of major healthcare legislation to agricultural workers in Arkansas, Maine, and Nebraska. Those states, of course, were carefully chosen. Senator Blanche Lincoln, Democrat of Arkansas and chairwoman of the Agriculture Committee, voted on Saturday to move forward with debate on the healthcare bill. But she has threatened to oppose it if big changes are not made. Lincoln has voiced particular concern over a proposed government-run health insurance plan, or public option, that would compete with private insurers.