They can't. They are a rich suburban white party who looks down on rural voters and working class voters. Thanks Obama!
No, democrats are happy to get rural voters. College-educated people in rural areas, unless the family of giant corporate farmers and executives thereof are as D as any other people. Think of schoolteachers and medical professionals. The blue-collar workers on corporate farms and in dairies, feed lots, and slaughterhouses are heavily non-voters such as non-citizens and Old Order Amish.
When the kids of the farm, dairy, feed-lot, and slaughterhouse workers start voting, then it is over for the Republican dominance in rural areas. Many of those workers are in business operations as regimented as assembly lines of the early twentieth century, and when they vote they will vote much for the political agenda most similar to the Democrats of the 1930's. The Republican party is still hostile to labor unions and has gained votes of working-class people as unions weaken. Just look at West Virginia.
Most rural Americans do not work on farms or have anything to do with agriculture at all.
Yes, but people working in rural dairies and slaughterhouses are in the agricultural economy. Dairy and slaughterhouse workers are heavily concentrated in assembly-line style work, and management operates much as it did in factories less connected to farmers' production.
Farming is the basis of the local economy, and such people as equipment dealers and repair people, schoolteachers, police and firefighters, attorneys, medical professionals, restaurant wait staff, retail clerks, insurance agents, and tax collectors know this well.