If the economy is starting to stall, the president can't just sit there. He has to stimulate—turn it on, bring it to life, perk it up. You can stimulate practically anything: a person, a conversation, a mind, or even the growth of a plant.
Stimulate is often used to describe a physical or sexual sensation, but don't get bogged down in that kind of thinking. Often, a government will try to stimulate economic activity by creating a stimulus package. Or, say, for example, that I'm trying to sell my new song CD. In order to stimulate interest, I need to send out a sample song to all my friends. Unless, of course, my songs are no good.