Public sector unions are not just the base of the party — they’re the base of the base. As the 2010 campaign has ground on, other supporters and donors, notably Wall Street, have abandoned Democratic candidates. But unions representing teachers and state and local employees have doubled down. According to the Wall Street Journal, the National Education Association, the largest U.S. teachers union, spent more than $3.4 million on ad buys and direct-mail campaigns for the key electioneering period from Sept. 1 to Oct. 14. The American Federation of State, County and Municipal Employees spent $2.1 million in that period. Union members and their families are key to the Democratic “ground game” for Nov. 2.

But in an era of increasing discontent over taxes, government spending and the perks of government employees, these are not necessarily the allies you want to have. A party that depends on the public employees to get elected will have trouble reaching out to the wider electorate — i.e., the people who pay the taxes that support public employee salaries and pensions.