WHAT IF…. Over the last several months, Joe Lieberman has been anything but consistent on health care reform. He’s been all over the map on explaining his opposition to the public option; he’s signaled support and opposition to a Medicare buy-in; he’s said he does and doesn’t want to see health care reform get done this year, etc.

But there’s one thing Lieberman has been entirely consistent on: whatever the left is for, he’s against.

It’s obviously just a thought experiment, and we’ll never know for sure, but I wonder what would have happened if liberals had said the Medicare buy-in/public-option trigger was a wholly unacceptable compromise.

In general, some of the leading progressive reform proponents said the opposite.

Rep. Anthony Weiner (D-NY), one of Congress’ fiercest supporters of the public option, has come out to support the Medicare buy-in proposal in the Senate Democrats’ deal.

“This is one idea I like a lot,” Weiner said in an email to the Daily News, calling the idea “remarkable.” […]

It’s a plan that “would perhaps get us on the path to a single payer model,” Weiner said. “In a debate that hasn’t focused enough on how to genuinely contain costs and deliver affordable health care, this is one idea I like a lot.”

Around the same time, Howard Dean expressed some support for the compromise framework, and Sen. Bernie Sanders (I-Vt.) said the compromise may be even “better” than the watered-down public option.

Just for the sake of discussion, what if Weiner, Dean, and Sanders had all expressed disappointment with the Medicare buy-in compromise? Would Lieberman — who not only ran on a Medicare buy-in platform in 2000, but also signaled some preliminary support for the idea last week — be willing to kill reform over the idea now?

Obviously, this presumes that Joe Lieberman is a small, bitter man, who puts foolish vendettas over the interests of his constituents and his country. Given the circumstances, that doesn’t strike me as an outrageous stretch.

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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.