Apple - How can I force an app to redownload from Mac App Store?

Answering my own question. I enabled the debug menu and then selected Reset Application, restarted the App Store and now the Download button shows up again.

To enable the debug menu, open Terminal and run

defaults write com.apple.appstore ShowDebugMenu -bool true

First, make sure that you do not have a copy of that app on another hard drive that is mounted.

Next delete the icon from Launch Pad. It works like iOS where you click and hold on the icon until they start jiggling and then click the X button to delete it.

Quit and restart the Mac App Store.

Now you should see that it is available to download in the Mac App Store.