PUBLIC OPTION WATCH…. Especially now that the Senate Democratic caucus has 59 members, and it’s unclear whether any of its members would support a Republican filibuster of health care reform, it’s helpful to know which Dems are on board with a public option, and which aren’t.

On Wednesday, Sen. Mary Landrieu (D) of Louisiana seemed to join Joe Lieberman in the group of caucus members opposed to an optional public plan. Asked under what circumstances she would support a public option, Landrieu said, “[V]ery few, if any. I’d prefer a private market-based approach to any health care reform that would extend coverage.” She said covering the uninsured would be “nice,” but said “but it would be immoral to bankrupt the country while doing so.” (Since a public option would lower costs, Landrieu’s argument doesn’t make sense.)

Yesterday, meanwhile, Sen. Mark Warner (D) of Virginia signaled support for a public option. His spokesperson made it seem as if Warner isn’t an enthusiastic supporter of the idea, but unlike Landrieu and Lieberman, Warner would support a bill if it included the provision: “It’s not a make or break thing — he wants to see a health reform bill that contains costs, and if it includes a public option … he would vote for it.”

Sen. Kay Hagan (D) of North Carolina has already supported a public option in the Senate HELP Committee bill, but she’s signaled a willingness to negotiate it away.

As a member of the Senate Health, Education, Labor, and Pensions Committee, Sen. Kay Hagan (D-NC) voted in favor of a health care reform bill with a public option. But she’s also interested in a compromise that would scrap the public option in favor of system of private, state-based, non-profit health-care cooperatives. “Having been a state senator for 10 years,” she said, “I think states can do a good job at that.”

Kay Hagan’s vote for the public option wasn’t easily won, so it’s little surprise that she’s open to alternatives.

True, but here’s hoping Hagan and her colleagues remember what Republican leaders have said about concessions — whether reform advocates keep or scrap a public option and/or a co-op plan, the GOP will oppose the legislation.

When two competing sides have the same goal in mind — reforming a broken system — compromise is possible. When two competing sides have opposite goals in mind — one wants to pass reform, one wants to kill it — compromise isn’t possible.

Hagan has already supported a public option, and I’m glad. But if she thinks flexibility on the issue may generate broader support for the larger goal, she’s going to be disappointed by the Republican response.

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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.