This is very good news. Many have feared that, with the Paul Ryan plan to end Medicare getting so much attention, Congress would downshift to a safety valve, the Paul Ryan plan to cripple Medicaid, as part of a deficit reduction deal. Under the Ryan plan, Medicaid would be turned into a block grant, which means that state policymakers would be allowed to change the program as they see fit, and that the program would not get funding based on need, but a flat amount that would not rise in a recession, when more people become poor and qualify for Medicaid. Experts estimate that tens of millions of people would lose Medicaid coverage as a result, and considering that fully half of the coverage expansion from the Affordable Care Act comes from increases to Medicaid, the increase in the ranks of the uninsured would simply be magnified.

But rather than roll over for this, enough Senate Democrats to sustain a filibuster have said that they won’t allow it.

Forty-one Senate Democrats have signed on to several letters vowing to oppose House Republicans’ proposed Medicaid overhaul, ensuring the proposal won’t get enough votes to clear a filibuster hurdle.

One letter, to President Obama, spearheaded by longtime Medicaid defender Sen. Jay Rockefeller (D-W.Va.), garnered 37 signatures. It makes clear that the senators will oppose proposals to cap federal spending on Medicaid, a program whose spending currently fluctuates with need.

Four other senators — Dianne Feinstein (Calif.), Mark Udall (Col.), Michael Bennet (Col.), and Amy Klobuchar (Minn.) — wrote separate letters to the president.

This basically becomes a firewall against severe changes to Medicaid. And not one Democrat in either chamber signed on to the Ryan budget and its changes to Medicare.

There’s still one option to guard against; Congress could use the budget reconciliation process to pass a budget that messes with Medicaid while leaving these 41 Democrats behind, requiring only 50 votes. But the numbers for such a deal would be difficult to find, because there are probably at least a few Republicans – Rand Paul, Mike Lee, Jim DeMint – who wouldn’t sign on to any deal that doesn’t abolish government altogether.

Overall, it’s good at this stage for 41 Democrats to plant a flag and say they won’t support the block granting of Medicaid. This complicates the Biden negotiations; if Medicare, Medicaid and taxes are off the table, there’s just not that much left.

UPDATE: Jay Rock is leading this effort. Here’s his interview with Ezra Klein.