Answer:
Smith's opponent could use "soft money" to pay for the ad and does not have to claim support for it.
Step-by-step explanation:
Soft money is money that is donated to political parties where the purpose is not to promote a specific candidate. Soft money is largely unregulated, and there is no cap on it. Political parties can essentially spend it on whatever they want as long as it fits a generic objective to "increase the vote." Soft money is often called "nonfederal" contributions.
The opponent might be using these funds to sponsor a slander campaign against Smith.