Bernie Sanders pulled out an old photograph signed by Hillary Clinton to make a point in the two candidates' ongoing battle over health care policies.

The Vermont senator has been fielding attacks on his health care stance from the former secretary of state's presidential campaign for days and responded with a simple tweet Wednesday.

The photo, apparently signed by Clinton during the first year of Bill Clinton's presidency, had the message: "To Bernie Sanders with thanks for your commitment to real health care access for all Americans and best wishes."

Clinton has been pushing back on Sanders' long-held support for a single-payer health care system, in which the government pays for health-care costs rather than private insurers.

Chelsea Clinton, who has been campaigning on her mother's behalf, said Wednesday that Sanders would take away health care from millions of Americans by dismantling Medicare and Medicaid.