The GOP message on the sequester is awfully muddled. Some Republicans argue it will gut the military and kill jobs, while others argue that Democrats who claim it will gut the military and kill jobs are alarmist, that the sequester won’t be any big deal, and that we should just let it hit. Those in the latter category like to wave around the talking point that the sequester will only cut 2.5 percent of federal spending.

But a new report coming out today will debunk the idea that the sequester will have such a minimal impact. The study, from the liberal-leaning Center on Budget and Policy Priorities, will find that in practical terms, the sequester will cut more than five percent out of the budgets of many discretionary and mandatory non-defense spending programs, and nearly eight percent out of the budgets of all discretionary defense programs. And in many cases it will be worse than that, the study will note, because those cuts have to be crammed into the remainder of the 2013 fiscal year.

The reason: The 2.5 percent talking point is based on the fact that the sequester will cut roughly 2.5 percent out of all federal spending. But the sequester doesn’t hit all federal spending. Rather, it is mostly targeted towards discretionary spending (and some mandatory non-defense spending). So the sequester cuts as a percentage of the spending they actually will target is a lot higher.

CBPP’s report, to be released later this afternoon, will take the total $85 billion in sequester cuts and apply it across the board to all discretionary spending for the remainder of fiscal year 2013, which ends on September 31. It will find:

* The sequester will result in a 5.1 percent cut to all non-defense discretionary spending. That includes everything from Head Start to housing to cancer funding to border patrols to national parks to education to the Federal Aviation Administration, and a lot more.

* The sequester will cut 7.7 percent from all discretionary defense programs.

* The sequester will cut 5.2 percent out of all the non defense mandatory spending it targets (some areas, such as Social Security, Medicaid, food stamps, and others, are exempt). That cut will hit farm price supports, emergency unemployment benefits, grants to states for social services, and more.

In some cases, the cuts could be worse than the numbers suggest (for various complicated reasons it depends on the program), because they will be inflicted on the programs within the seven month period from now until September 30th.

In one sense, the battle that will unfold when the sequester hits may be valuable: It will help illuminate the true nature of public opinion towards government and federal spending. It is a basic fact about our politics that people tell pollsters they want government cut in the abstract but suddenly turn on spending cuts when pollsters begin to ask them about specific policies they like. We’re about to see how Americans will react when a huge range of specific government services they rely on daily — not to mention a massive amount of spending on federal jobs — are suddenly scaled back right beneath their feet.

More from PostOpinions:

Vanden Heuvel: The human cost of the sequester

Sargent: How pundits enable Republicans

Capehart: An ‘unfair’ assessment of Obama’s leadership

Samuelson: Are we creating a lost generation?

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.