I spent some of the morning watching the webcast of the event the Committee for a Responsible Federal Budget put on to promote their paper testing the fiscal responsibility of the various GOP presidential candidate’s plans. Alice Rivlin — who is truly the budget wonk’s budget wonk — made a number of good points, as she always does. But she also made one comment worth challenging.

After saying that “there is no solution that does not include bending the cost curve on health care, putting Social Security back on track, and raising more revenue from a reformed tax system,” she went on to comment: “I don’t expect Republicans to raise taxes. But one definition of responsibility is to see if you can reform the tax system in a way that doesn’t make things worse. And on that score, all these candidates fail.”

I call this the Republican budget curve, and it pops up in budget conversations all the time. The argument, basically, is that the Republican Party’s attitude toward revenues has become so extreme that no individual Republican can be expected to challenge it, and therefore, the budget proposals of individual Republicans should be graded on a curve that assumes proposing new revenues is impossible.

But it’s not impossible. Senators Tom Coburn, Saxby Chambliss and Mike Crapo endorsed raising revenues in the Gang of Six framework. The Republicans who served alongside Rivlin on the Bipartisan Policy Center’s debt task force endorsed higher revenues. The Republicans who served on the Fiscal Commission and voted for the Simpson-Bowles proposal endorsed higher revenues. And that’s because every serious effort to figure out how to significantly reduce debt ends up at the same conclusion, the one Rivlin pointed to: Revenues need to be part of the solution, just as spending cuts do. Sen. Kent Conrad likes to show this graph, and it’s worth reposting here:

Which isn’t to say it’s not difficult for elected Republicans to admit that taxes need to rise. The Club for Growth might primary you. Grover Norquist will come after you. But being responsible is difficult. No Democrat who says Medicare and Medicaid and Social Security can’t be cut can be considered fiscally responsible. And no Republican who pledges to oppose all tax increases, regardless of circumstances, can be considered fiscally responsible. There’s no curve here. There’s only math. And politicians who want to be applauded as “responsible” can’t be permitted to ignore it.