In order to get its temporary debt limit suspension passed, House GOP leaders had to promise House conservatives a budget that cuts spending so deeply — with no new revenues, natch — that it wipes out the deficit in 10 years.

What would such spending cuts look like in the real world? Hint: Insane.

I asked the liberal leaning Center on Budget and Policy Priorities to run the numbers. The result: Such a plan would require downsizing much or all of the federal government by anywhere from one-sixth to one-third.

Here’s how it works. Richard Kogan, a senior fellow for the CBPP, estimates that in order to balance the budget in the year 2023, you’d need to come up with about $775 billion in cuts out of overall government program spending of $5.2 trillion. (That number, which could be higher or lower since conditions can change, is based on calculations taking into account new revenues from the fiscal cliff tax hikes and interest savings CBPP projects.)

What would coming up with $775 billion entail? There are three permutations.

1) If you take out Social Security, Medicare, and defense, achieving these savings would require a 37 percent across the board average cut to all other federal spending, Kogan projects. (That’s a reasonable starting point because Republicans say we can’t cut defense, or entitlements for anyone over 55.)

That is an enormous cut. That’s a 37 percent cut to everything from veterans’ pensions and benefits to disability for the aging poor to education to scientific research to transportation to foodstamps.

2) If you only exempt defense spending, and include Social Security and Medicare as targets for cutting, that would still require a 17 percent across the board cut to those major entitlements and all of the rest of the federal government’s programs, Kogan estimates. (That’s also a reasonable starting point, since Republicans have said we do need some entitlement cuts impacting  those under 55.)

3) If you include everything — entitlements, defense, etc. — you still have to downsize the entire federal government by 15 percent to get those savings, Kogan projects.

Every one of those permutations requires enormous cuts to government programs benefiting millions and millions of Americans — the poor, sick and elderly included — and having an untold impact on the country. This all but ensures that whatever budget Republicans do produce wiping out the deficit in 10 years will not go into much detail about specific cuts, since the above demonstrates that so doing would be a political impossibility. As noted by Jonathan Chait, whose post gave rise to this one, it will inevitably be loaded up by magic asterisks and phantom savings.

Now, Republicans will object that such deep cuts don’t have to be applied uniformly across the board. Just as they did during the battle over the Ryan budget and over Mitt Romney’s proposals, they will simultaneously refuse to detail where their spending cuts would be focused while insisting any efforts to nail down the true mathematical implications of their proposals — by, say, extrapolating what they would mean if replied uniformly across the board — are automatically misleading.

But as the last election showed, Democrats have cracked this code. Dems fully acknowledged that they were making such assumptions, while noting that those assumptions were made necessary by the Republicans’ refusal to detail specifics. Judging by the election results, it worked, and the GOP effort to obscure the true fiscal implications of their own stated goals didn’t. Given the political impossibility of proposing specific cuts of the above magnitude, Republicans will have to go the obfuscation route again. Which simply means that in extending the debt ceiling, Republicans have exchanged one fantasy for another.