However, if the debt rescheduling causes losses on loans held by European banks, it weakens the private banking system, which then puts pressure on the central bank to come to the aid of those banks. Private-sector bond holders are an integral part of the public and private banking system. Another possible response is for wealthy member countries to guarantee or purchase the debt of countries that have defaulted or are likely to default. This alternative requires that the tax revenues and credit of the wealthy member countries be used to refinance the previous borrowing of the weaker member countries, and is politically controversial.