His actions have largely faded from memory, but Sen. Joe Lieberman (I-Conn.) singlehandedly killed one of the best ideas of the health care reform fight. Democrats were prepared to trade away the public option to balking centrists, and in exchange, Medicare’s eligibility age would drop to 55. Liberals and centrists both approved, and polls showed broad popular support for the idea.

Lieberman said he’d kill the entire health care reform initiative unless the idea was promptly removed. Left with no choice, Democrats agreed. He couldn’t explain why he opposed the measure, or why he’d endorsed the same idea just a few months prior.

Given this background, I’d just as soon see Lieberman steer clear of Medicare forevermore, but the retiring senator returns to the subject in an op-ed today, presenting his plan to “save” the health care program. It’s a pretty thin plan, which does very little to control costs — he doesn’t even reference the Independent Payment Advisory Board — suggesting that Lieberman, like Republicans, is more interested in shifting burdens onto seniors and their families.

But here’s the part that’s likely to get the most attention.

…I am drafting legislation that will preserve Medicare without privatizing it by saving at least $200 billion in Medicare spending over the next 10 years and extending Medicare’s solvency by approximately 20 years. These figures are based on estimates by the independent Congressional Budget Office of ideas comparable to the ones I am proposing.

First, I will propose raising the Medicare eligibility age every year starting in 2014 by two months until it reaches 67 in 2025.

Lieberman is clearly moving in the wrong direction. He went from wanting to expand eligibility, bringing more people into Medicare, to restricting it, keeping more people out.

As Paul Krugman explains, such an approach is needlessly cruel.

[T]hink about what it means to move people out of Medicare into private insurance, if they can get it.

Medicare has its problems — but all the evidence says that it is substantially more cost-effective than private insurance. Partly this is because it has lower administrative costs; partly it’s because Medicare is able to use its market power to negotiate lower prices. And the international evidence is overwhelming: single-payer systems are much cheaper than systems centered on private insurance.

So think of this as a national interest thing rather than a budget thing: Lieberman is proposing that we move a substantial number of older Americans into a worse, more expensive health care system. Why would you want to do such a thing, as opposed to raising enough additional revenue to keep them on Medicare?

This was too often overlooked in 2009, but lowering eligibility and allowing more Americans to get into the Medicare system strengthened the program.

Lieberman’s contribution to the debate isn’t nearly as helpful as he thinks it is.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.