And so it begins. House Republicans have vowed to cut $100 billion from the federal budget. Of course, they're making exceptions for Social Security, Medicare, defense, and homeland security. Which means that the tiny slice that remains has to be subject to a 20% cut or more.

And then, when you start to look at the programs they plan to cut, all of them either have strong lobbies, strong policy rationales, or both. Here's George Will a couple days ago making the case that Republicans should not cut funding for scientific research. And there's a furious (and also persuasive) response against cutting transportation infrastructure:

Groups that back more highway spending aren't waiting to see specific cuts to register their opposition. Congress is expected to take up a new multi-year highway and transportation funding bill this year, and a diverse array of groups ranging from the Chamber to big labor unions are calling for more funds to rebuild the nation's infrastructure.

The Chamber, which contributed heavily to GOP congressional candidates in the midterm elections, said in a letter last week that subjecting highway spending to the uncertainty of annual budget cuts would lead to more job losses in the battered industry. The letter was also signed by groups tied to the construction industry.

And on and on down the line. So now Republicans are cutting their spending cut target in half:

Many people knowledgeable about the federal budget said House Republicans could not keep their campaign promise to cut $100 billion from domestic spending in a single year. Now it appears that Republicans agree.

As they prepare to take power on Wednesday, Republican leaders are scaling back that number by as much as half, aides say, because the current fiscal year, which began Oct. 1, will be nearly half over before spending cuts could become law.

They haven't even taken over yet, and they've already reduced their target by half! They will reduce it further still as they get into the details. The one thing that won't be scaled down is the Republican appetite for tax cuts.

The basic situation is that you have a tiny handful of principled conservatives who genuinely want to cut the size of actual government programs. But that accounts for a tiny slice of the general opposition to government programs, which is rooted in misperceptions about what government spends money on alongside strong support for the programs that actually exist. Government programs are popular. Some of them serve little purpose (think farm subsidies) but those generally exist precisely because they have powerful constituencies.