I hate to keep posting this, whenever I hear about the Democrats and Wal-Mart, as it smacks of spamming - but it does bear repeating (and would make a perfect t-shirt or bumper sticker): "only a jackass would rail against Wal-Mart, and then ask for the votes of its customers."
They are not after the customer's votes. They are after the worker's votes, and those of Wal-Mart's competitors.
The interesting thing is that Hillary would send back money. Apparently, she thinks the unions who are fighting Wal-Mart are of greater value to her than Wal-Mart campaign contributions.