As discussed here previously, the majority of Republican presidential aspirants propose substantially increasing the defense budget in one way or another. Few explain, however, how they plan to pay for their proposed increase. James Gibney, a former foreign service officer and speechwriter for Secretary of State Warren Christopher, noted the disconnect in an opinion piece for Bloomberg View last week. And while Gibney’s contention that “there is a strong case for increasing the defense budget” is debatable, he is absolutely correct that such a case “has to be grounded in political and economic reality.”

The reality is that, as much as Republicans wish to pretend it was otherwise, the defense budget is one priority among many when it comes to distributing government funds. Many national security hawks argue that the defense budget is not the primary driver of the country’s debt problem. And they are right. Entitlement programs are the main cause of national debt. However, entitlement programs also enjoy a great deal of popular support. As recently as December 2013, Pew found that the American people supported maintaining entitlement programs and aid to the poor at higher levels than increasing the defense budget. Over half of those surveyed said that the government should focus on deficit reduction, with only 40 percent supporting increased military spending. National security has taken on a renewed resonance with voters in light of events such as the crisis in Ukraine and the rise of ISIS, but as of May 2015 the economy remains voters’ primary concern going into the next election.

Gibney also notes the habit of Republican candidates to invoke the name of Ronald Reagan, as well as their consistent failure to grapple with the fiscal impact of the Gipper’s defense buildup. He writes:

During Reagan’s eight years in office, according to the historical tables of the 2015 U.S. budget, national defense accounted for an average of 26 percent of all federal spending, and 5.7 percent of gross domestic product. By contrast, the Obama administration’s national defense spending over the last six years seems anemic: an average of 18.8 percent of federal outlays, equal to 4.25 percent of GDP.

But here’s the rub: During the Reagan years, the U.S. government was also taking in an average of 17.6 percent of GDP a year in tax revenue; the Obama administration has taken in an average of 15.6 percent a year. Even so, thanks to a combination of tax cuts and defense spending increases, Reagan oversaw a ballooning of U.S. debt from 25 percent of GDP in 1981 to 40 percent in 1988.

The Pentagon’s budget was 30 percent higher in 1986 than it was when Reagan took office in 1981. Despite his rhetoric criticizing welfare, the fortieth president made relatively small cuts in domestic programs over the same period. The increased defense spending thus caused deficits to skyrocket and federal debt to double over the first five years of his presidency.

Republicans face a similar problem: the increases they seek in defense spending will not take place instead of current entitlement spending, but in addition to it. For example, if Louisiana Governor Bobby Jindal has his way and Pentagon’s budget reaches four percent of gross domestic product by 2020, the $260 billion he would spend above the Budget Control Act cap for that year would come in the form of deficit spending.

Gibney thinks the only way out of this quandary is for Republicans to walk back their commitment not to raise taxes. But that solution assumes that it is necessary to increase the defense budget. While perfect safety is always an illusion, the United States has inherent advantages in geography, and a sizable lead in defense spending over its nearest rivals. If Republicans think the military is not as effective as it once was, they should look at the Pentagon’s internal allocation, rather than extracting more wealth from the American people or adding to the country’s debt burden.