CLEARING ONE HURDLE, RUNNING INTO ANOTHER…. Yesterday, House Energy and Commerce Committee Chairman Henry Waxman (D-Calif.) came to an agreement with four conservative Blue Dog Democrats on health care reform, clearing the way for approval. It took a while, but the biggest hurdle between reform and House passage had been cleared, and Waxman scheduled a mark-up for yesterday afternoon.

But it was delayed once more. This time, the left balked.

House Speaker Nancy Pelosi spent half of Wednesday finalizing a deal with the Blue Dogs — and the other half quelling a brewing rebellion among progressives who think conservatives have hijacked health care reform.

Liberals, Hispanics and African-American members — Pelosi’s most loyal base of support — are feeling betrayed after House Energy and Commerce Committee Chairman Henry Waxman (D-Calif.) reached an agreement with four of seven Blue Dogs on his committee who had been bottling up the bill over concerns about cost.

The compromise, which still must be reconciled with competing House and Senate versions, would significantly weaken the public option favored by liberals by delinking reimbursement rates to Medicare.

The seriousness of the concessions Waxman made to win over Blue Dogs is itself open to debate. Jonathan Cohn described changes as “modest,” and said, “Most of the bill’s core elements seem to be intact, including the public insurance option.” Cohn added that the deal is “a pretty big step forward” and said the House bill is on track to be “very good legislation.” Ezra Klein’s analysis was similar, noting that the “substantive changes” made to the compromise bill “are minimal.”

As of last night, several liberal Dems strongly disagreed. Rep. Jerry Nadler (D-N.Y.) called the deal “unacceptable.” Rep. Barney Frank (D-Mass.) said he’s not prepared to vote for the bill. Rep. Lynn Woolsey (D-Calif.) said the bill needed to get “much stronger” to earn the support of the Congressional Progressive Caucus, and raised the prospect of scrapping the entire legislation and starting over.

Waxman nevertheless seems confident the process can get back on track today. He’s scheduled a 10 a.m. (eastern) mark-up, and will host a “mass question-and-answer session” for the entire caucus, in which he hopes to alleviate concerns.

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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.