Yes, once. Under president Reagan (!!) Congress passed and he signed a prescription drug plan for Medicare beneficiaties. It was financed in a horribly expensive and oppressive way that caused its beneficiaries to revolt and Congress repealed it. ObamaCare is equally, or more, unpopular, meaning we have a decent shot at repealing it.
It was not Drug coverage - it was Catastrophic coverage and a superior program. Stupid seniors decided $5.00 was a premium too far. Premiums for Medicare have increased anyhow.
http://www.theatlantic.com/business/archive/2009/09/catastrophic-medicare-reform/26666/
Medicare Catastrophic Coverage Act of 1988. Unlike killing Medicare Advantage, this enjoyed broad bipartisan support. Democrats liked expanding coverage for seniors and the disabled. Republicans were happy as long as you paid for it, and thought it would boost their image with seniors. The AARP gave it the big thumbs up. All sides had to stage a dramatic retreat a year later because seniors screamed bloody murder over the premiums. The benefits were actually pretty useful, but deficit neutrality was political suicide.