Story highlights "Well, I don't know where he was when I was trying to get health care in '93 and '94," Clinton said of Sanders

The problem: Sanders attended an event with her to push health care reform in 1993 and introduced his own single-payer health care plan in March of that year

St. Louis (CNN) Hillary Clinton on Saturday questioned where Vermont Sen. Bernie Sanders was when she was fighting for expanding health care as first lady in 1993 and 1994.

"We are going to pull together and stay together and stand up against those powerful forces. And I always get a little chuckle when I hear my opponent talking about doing it," Clinton said at an event here. "Well, I don't know where he was when I was trying to get health care in '93 and '94, standing up the insurance companies, standing up against the drug companies."

The problem: Sanders attended an event with her to push health care reform in 1993 and introduced his own single-payer health care plan in March of that year. And Clinton wrote him a hand-written thank you note for his work on the issue in 1993.

Some of Sanders' aides quickly tweeted a photo on Saturday of Sanders standing behind Clinton at an event at Dartmouth College on December 7, 1993

"I am grateful that Congressman Sanders could join us today from Vermont," Clinton said at the event.

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