Yes, the game is attached to your account, you can redownload it as often as you like. It's not bound to a computer or an operating system, so if you format it, put a new winodws on it, or if you exchange parts or buy a new computer, then this does not matter, you can always redownload it.
Backing up the files is allowed, and Steam has somewhere a built in utility. So if you're formatting, you're not forced to stress your internet connection, you can make before a backup to an external HDD, or so.
IIRC there shouldn't be a separate installation file, should go all via Steam.
And o_O about the prime minister. I remember that discussion before the release.