The Republican plot to slash Social Security has moved to the Senate. After House Republicans changed the rules to ensure that the disability side of the program (SSDI) will run out of cash in late 2016, it was the Senate GOP's turn to bash the program in a Budget Committee hearing.

They say that Social Security is fundamentally flawed. We can't transfer money from the retirement side to the disability side, because that would be financially irresponsible. They frame this as "robbing Peter to pay Paul," which is apparently the slogan of choice, since it was repeated by several GOP senators at the hearing. The SSDI fund will "soon be broke," said committee Chair Mike Enzi (R-Wyo.) "I'm really tired of bailing out water," said Sen. Lindsey Graham (R-S.C.).

This is a bunch of nonsense. It is designed to obscure a pure ideological agenda of cutting benefits. And Democrats, including President Obama, should not play along.

First, SSDI is not "broke." Even without the trust fund, it can pay over 80 percent of current benefits. The retirement side of Social Security is fine until 2034, and topping up SSDI out of that money would only shave one year off that. Michael Hiltzik has a full breakdown of Social Security's finances.

But there's a bigger problem here. In our boneheaded political culture, doing things for future generations counts as the height of responsible policy-making. We have to cut the deficit on account of the children, Very Serious People are always saying.

It's an obnoxious pose, since it writes off the travails of, you know, the living. But in a deep sense it's not very feasible. No financial projection has perfect foresight, and today's Congress cannot bind the hands of future Congresses. For example, when the government got the national budget briefly into surplus under Bill Clinton in the late 1990s, a new government under George W. Bush reversed course and gave most of the proceeds to the rich.

Generally speaking, the same principle holds for retirement. We can't "fix" Social Security right now with a magic-wand policy. It will always need to be maintained.

So let's restate the principles behind Social Security. First, old and disabled people should not have to work. Therefore, we provide them with a stipend to live on. It has been an enormous success, cutting elderly poverty by 71 percent.

The problem we face with Social Security is, for the most part, simple demographics. People are getting older, and therefore there are more not-working people per current worker. What to do about that situation clearly depends on two factors: our ability to pay, and a judgment about the worthiness of the people getting Social Security.

As for the first, maintaining Social Security indefinitely would cost about 1 percent of GDP over the long term. That is half the cost of the Bush tax cuts — something the nation can easily afford. The second is what's driving this entire debate. Republicans don't think people on SSDI are deserving, and are trying to claw back some of the benefits. As such, they've begun a campaign of anti-SSDI agitprop, coupled with a blizzard of irrelevant accounting argle-bargle to obscure their real motivation.

But conservatives must be made to own this. No Democrat should give them political cover as part of a bipartisan bargain to raise the payroll tax and cut benefits, as President Obama has repeatedly come close to doing. Republicans control both houses of Congress, so if they believe SSDI benefits are too high (at a whopping $1,165 per month), then they should pass legislation to that effect.