You might have thought that the lesson would be obvious. In the past year, we’ve had an elementary tutorial in the uses of raw military power: in Ukraine, where Russia manufactured a “rebellion”; in Iraq, where the Islamic State expanded its footprint; and in Asia, where China harassed ships of nations claiming islands China considers its own. But the implications of these events seem to have escaped the Obama White House and Congress.

They are systematically reducing U.S. military power as if none of this had happened. Defense spending has become just another line item in the budget, increasingly disconnected from our strategic interests and potential threats. It’s a money pot of possible reductions to pay for burgeoning retirement benefits, mainly Social Security and Medicare, which are largely immune to cuts.

Our strategic needs are twisted to fit available defense dollars, as opposed to defining realistic military missions and then estimating their costs. An example: The Pentagon rules out future “prolonged stability operations . . . on the scale of Iraq and Afghanistan.” Big savings! Unfortunately, it’s easy to imagine such a need: say, a lengthy occupation of Middle East oil fields on which the world economy depends.

Defense makes a tempting target for budget-cutters. Until it’s used, military power is mostly invisible, so the general public doesn’t notice reductions. Nor is defense spending especially popular. A recent Gallup poll found that 37 percent of respondents thought it too high and 28 percent too low (most others judged it about right). Disappointments with the wars in Iraq and Afghanistan — where military successes were offset by diplomatic failures — compound disillusion.

Unsurprisingly, the Budget Control Act of 2011 (BCA) took nearly $1 trillion out of then-projected military spending over a decade by imposing annual caps on the defense budget. These cuts are huge. In a new study, Todd Harrison of the Center for Strategic and Budgetary Assessments, a nonpartisan think tank, reports:

● Since 2010, inflation-adjusted defense spending has declined 21 percent. This includes spending in Iraq and Afghanistan, called “OCO” for overseas contingency operations. Without OCO, the drop is 12 percent.

● Defense spending in 2014 — including OCO — is 3.4 percent of the economy (gross domestic product) against a post-World War II average of 5.5 percent. If the BCA’s spending caps remain, defense spending in 2019 will fall below 2.5 percent of GDP, the lowest since 1940.

● Defense is 16.3 percent of the federal budget in 2014. Social Security is 23 percent, and Medicare 14 percent. They are growing while defense is shrinking.

There are more missions and fewer resources. Despite the cuts, Harrison thinks that the Pentagon’s present spending could require at least $200 billion more than the BCA’s caps allow over the next five years. Without higher caps, there will be more reductions in “personnel, acquisitions and readiness.” Already, the Army is being cut from an Iraq-Afghanistan peak of 566,000 to about 450,000. Under today’s caps, that might have to drop to 420,000.

Meanwhile, potential missions multiply: fighting terrorism; deterring cyber-attacks; protecting Europe (after Vladimir Putin’s Ukraine gambit, more troops are needed there); coping with Iran’s nuclear program; containing North Korea; maintaining open shipping lanes; dealing with a resurgent China (termed “the pivot to Asia”). Harrison chides the administration for neither spending enough to meet its strategic goals nor downsizing the goals to fit smaller defense budgets.

More scathing is a unanimous report from a congressionally mandated task force, the National Defense Panel. It warns that defense cutbacks “constitute a serious strategic misstep [that has] caused significant investment shortfalls in U.S. readiness and . . . have prompted our current and potential allies and adversaries to question our commitment and resolve.” The report wasn’t the work of cranks. The panel was co-chaired by William Perry, defense secretary in the Clinton administration from 1994 to 1997, and retired four-star general John Abizaid; it also included Michèle Flour­noy, President Obama’s undersecretary of defense from 2009 to 2012.

Since World War II, U.S. global leadership has rested in part on military might. It has often provided the stability that gave political and economic policies the time to succeed. Of course, military power has not always been used wisely or effectively — Vietnam being the largest failure. But the benefits of U.S. defense spending are often underappreciated because they flowed silently from wars not fought and global order maintained.

Higher defense spending is in our interest because global order is in our interest. Global order is hardly guaranteed, but without a strong U.S. military, the odds of global disorder are much greater. This fundamental national interest is being subordinated to short-term political interests — Republicans who won’t acknowledge that higher taxes are needed to pay for an adequate military; Democrats who will cut almost anything except retirement spending. History is likely to judge them harshly.

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