And how would he pay for his huge new defense budgets? In an interview with Fortune, Mr. Romney spoke of “enormous opportunities for finding efficiency and cost savings in the military.” His targets, according to his campaign, would be the Pentagon’s civilian work force and reforms of the weapons procurement process. Such reforms are necessary but not easy, given inter-service rivalries and the clout of Congress and a well-financed defense lobby.

The Obama administration has committed to similar reforms, which the Pentagon says will save $210 billion over six years. That’s a start, but still just a fraction of what would be needed to offset the added cost of Mr. Romney’s G.D.P.-linked budget. The truth is that the added military spending would have to come from savaging most other federal programs, including those serving the most vulnerable Americans.

Mr. Ryan, of course, is now on board with the Romney plan. But he voted for the 2011 Budget Control Act, which mandated $487 billion in defense cuts over a 10-year period beginning in 2012 and $500 billion more beginning in 2013 if Congress doesn’t reach a deal on reducing the deficit. And the budget he produced as chairman of the House Budget Committee is less generous to the Pentagon. It would, however, make severe cuts in diplomacy and foreign aid. Such budgeting would lead to even greater overreliance on military might than already exists.

After a decade of unchecked spending growth, the Pentagon can prudently absorb significant reductions at a time when the country is under economic stress. President Obama has begun to put the brakes on spending by slowing the rate of growth. But billions more could be saved by cutting wasteful or unnecessary conventional and nuclear weapons programs.

Voters are entitled to an honest debate on defense priorities. They need to hear not just about weapons and troop levels, but about the threats the candidates see in the world and how diplomacy and other levers of power can also be used to keep the nation safe. So far, they’ve heard nothing more than generalities from Mr. Romney and Mr. Ryan. Neither man has a background in national security, so it’s not surprising that they’re trying to prove their bona fides by embracing a profligate defense budget.