When the elected officials and bureaucrats who run a government want to stack the deck in favor of a politically connected special interest, they have three main ways that they can go about it:
They can subsidize the special interest, often using taxpayer cash.
They can penalize the competition of the special interest, often through tariffs.
They can mandate that people do business with the special interest.
Each of these actions is economically harmful as government-backed subsidies, penalties, and mandates all impose unnecessary costs on regular people. Worse, they often lead to predictable, if often unintended, consequences that do serious damage beyond what they do to personal finances.
In the case of ethanol in the United States, the federal government has employed all three measures over the years, frequently with bipartisan political support. Its subsidies keep afloat politically connected businesses that wouldn't otherwise be able to keep themselves in business.