Trump says he's boosting defense spending by $54 billion. The real number is $18 billion.

With President Donald Trump gearing up to formally unveil his budget blueprint Tuesday night, White House aides have been insisting that Trump will propose one of the biggest increases to the Pentagon budget in years. The problem is they’re using woefully misleading numbers.

Administration official have spent days telling reporters that Trump would call for increasing defense spending by an eye-popping $54 billion — a sum that would be particularly striking given that the US has largely wound down the long wars in Iraq and Afghanistan. It would be, in Trump’s words, “historic.”

Here’s the thing: It’s not. The actual increase is closer to $18 billion. Eagle-eyed defense hawks such as Arizona Republican John McCain have noticed the discrepancy, and they’re not happy.

“President Trump intends to submit a defense budget that is a mere 3 percent above President Obama’s defense budget, which has left our military underfunded, undersized, and unready to confront threats to our national security,” McCain said in a statement. “With a world on fire, America cannot secure peace through strength with just 3 percent more than President Obama’s budget. We can and must do better.”

Understanding McCain’s anger means understanding the government’s byzantine and sometimes baffling way of allocating money for national security. For help deciphering it all, I turned to Mark Cancian, a highly regarded Pentagon budget expert at the Center for Strategic and International Studies.

“These numbers were intentionally misleading,” he told me. “The increase is dramatic, but nowhere near as dramatic as people had been expecting — or hoping for.”

Trump’s magical Pentagon math

Talking to reporters Monday, Trump’s OMB head, Mick Mulvaney, said the administration’s fiscal year 2018 budget would include $603 billion in defense spending. That sounds like, and would be, a lot of money.

The first problem is that the comment was interpreted as referring to money literally and exclusively going to the Pentagon. That’s wrong: The figure also includes defense-related spending at other agencies, like the Department of Energy, which manages the nation’s nuclear arsenal.

The second and bigger problem is that the White House was making an apples-to-oranges comparison in terms of how the increase was actually being calculated.

At first glance, Trump’s math makes sense. The Budget Control Act of 2011 capped spending for the Pentagon, the Department of Energy, and assorted other national security agencies at $549 billion in 2018. Trump is proposing spending $603 billion in 2018 on those agencies. The difference between the two numbers is the purported $54 billion increase that the president and his aides have been trumpeting for days.

The problem is that Trump and his aides are comparing the wrong figures. Obama himself had called for blowing past the congressional spending caps and spending a total of $585 billion on national security, including $557 billion for the Pentagon and $28 billion for the Department of Energy and other related agencies. The actual difference between what Obama had projected spending and what Trump is now proposing is just $18 billion. That, Cancian notes, “is what John McCain is so angry.”

“It’s a much smaller increase than people first thought,” he added.

It’s not the only reason McCain may be skeptical about Trump’s budget blueprint. OMB head Mulvaney is a former Republican Congress member from South Carolina. In the past, he’s voted to cut billions from the defense budget and voiced skepticism about the enormous amounts of money the Pentagon receives every year. McCain voted against his confirmation as a result.

The Pentagon is so big that an extra $18 billion isn’t all that much

For almost any other part of the government, an influx of $18 billion would be cause to bust out the champagne. The State Department, for instance, has an annual budget of $50 billion — and Trump has talked about cutting 30 percent of that money to help pay for the new defense spending (a proposal that Republican Sen. Lindsey Graham said Tuesday would be “dead on arrival”).

But the Pentagon isn’t like most other parts of the government. For the Defense Department, $18 billion is an almost literal drop in the bucket.

Cancian said the Army alone has drafted a wish list for next year that amounts to $18 billion. Now the service will be lucky to get even a quarter of that money.

The relatively small size of Trump’s increase could also spell bad news for the Navy, which Trump has talked about expanding from 274 ships to 350, the largest buildup since the end of the Cold War. In a conference call Monday, an administration official said the money would go to new shipbuilding efforts and establishing a “more robust presence in key international waterways” like the Strait of Hormuz and the South China Sea.

Here, too, the problem comes down to dollars and cents. A report in the Hill last month noted that expanding the Navy’s fleet so dramatically wouldn’t come cheap. Experts quoted by the newspaper said it could cost as much as $165 billion over the next 30 years solely to purchase the new ships, submarines, and other boats. Maintenance and spare parts would cost even more. An extra few billion dollars would barely be a down payment.

The Navy wants a lot of new ships. It’s not clear Trump is ready to pay for them.

To be fair, Cancian noted that Trump will release a fuller budget proposal this spring that could call for massively increased spending for the Navy in the years ahead.

If so, that would be a major win for the Navy — and for Steve Bannon, Trump’s chief White House strategist. Bannon, who was recently given a permanent seat on the National Security Council, is a former Navy officer who believes war with China over its presence in the South China Sea is inevitable.

Beijing has spent the past several years building military bases — complete with airstrips, radar arrays, and advanced anti-aircraft weaponry — on a string of artificial islands. That, to Bannon, is part of a series of unacceptable actions by Beijing that Washington shouldn’t idly accept.

“We’re going to war in the South China Sea in five to 10 years,” Bannon said in March 2016. “There’s no doubt about that. They’re taking their sandbars and making basically stationary aircraft carriers and putting missiles on those. They come here to the United States in front of our face — and you understand how important face is — and say it’s an ancient territorial sea.”

That rhetoric, unsurprisingly, hasn’t gone over well in Beijing. According to the Guardian, the Chinese military issued a hard-edged statement on the day of Trump’s inauguration that warned about the prospect of war between the two countries.

“A ‘war within the president’s term’ or ‘war breaking out tonight’ are not just slogans, they are becoming a practical reality,” an official wrote on the website of the People’s Liberation Army, according to the Guardian.

Still, Trump’s proposed buildup may not set off the kind of arms race with Beijing that you might expect. The reason, though, isn’t particularly reassuring.

“They are building up so rapidly that it is hard to believe that anything we do could cause them to build even more rapidly,” Cancian said.