The Volcker Rule was designed to prevent commercial banks from engaging in speculative activities and proprietary trading for profit. This rule was a response to the 2008 financial crisis, during which risky trading activities by banks contributed to the collapse of financial markets. By prohibiting these activities, the Volcker Rule aims to protect depositors' funds and maintain the stability of the financial system. The rule specifically limits banks' investments in hedge funds and private equity funds, which are often associated with high levels of risk. Therefore, the primary effect of the Volcker Rule is to stop commercial banks from speculation and proprietary trading.

Choice A is incorrect. Enhanced witness protection is not a direct effect of the Volcker Rule. The Volcker Rule primarily focuses on limiting risky financial activities by banks, such as proprietary trading and certain investments in hedge funds and private equity funds, rather than enhancing witness protection.

Choice B is incorrect. While the Dodd-Frank Act does include provisions related to clearing houses, these are not directly related to the Volcker Rule. The rule's main purpose is to limit speculative trading activities by commercial banks, not necessarily promoting buying and selling of securities through clearing houses.

Choice D is incorrect. The establishment of the Consumer Financial Protection Bureau (CFPB) was indeed a part of the Dodd-Frank Wall Street Reform and Consumer Protection Act but it was not a direct result of implementing the Volcker Rule. The CFPB was created to protect consumers from deceptive financial practices whereas the Volcker rule specifically targets risk-taking activities by banks.