Why does U.S. need even more billions for the world's largest military?

With just 5 percent of the world's population, U.S. taxpayers pay for almost half the world's military spending. 

President Trump says it's not enough; his new "America First" budget calls for stripping civilian programs to add $52 billion to last year's $587 million military budget. Sen. John McCain, R-Ariz., wants to add $60 billion.

Trump's increase "is no shock. The President told us what he was going to do. And I think the McCain plan is more likely to get passed," analyst Brian Ruttenbur, senior analyst for Philadelphia-based Drexel, Hamilton & Co., told me after reviewing Trump's budget highlights today.

Despite all the spending, "the U.S. military is at Carter-esque levels," as it was when exhausted by the Vietnam War, Ruttenbur told me.

While Special Forces and troops from the 82nd Airborne division are fighting in Iraq and nearby countries, "the 101st Airborne is only at a third of its fighting force," for example, he said.

"We've been fighting these asymmetric wars against terrorists, house to house, for the past 15 years. We haven't been preparing for open warfare," fighting the Russians with tanks, or the Chinese with ships. "So we have equipment issues. Training issues."

But we still need way more? "The problem is, we still have a World War II doctrine. That means we have to be able to fight two all-out wars simultaneously, in the Pacific and the Atlantic and win in both places. But instead we've been fighting terrorists in the desert."

So the Republicans want to be able to do it all. Once we have bigger forces, will we go ahead and fight more wars? I asked.

"We have to be prepared for that," Ruttenbur said. "You know about the 'Asia pivot'" in U.S. policy, from the Middle East, to Asia? "How do you stop the Chinese from building islands, except you put your warships over there and say, 'Don't do that?' " Or the Russians from invading the Baltic countries, our smallest European allies?

"The problem is we've cut, cut, cut," after Congress tried to freeze spending  following the 2008-09 financial crisis and budget-crushing borrowing.

"So we haven't been doing the maintenance training needed. This buildup is a very Reagan-esque thing to do. We have 280 ships. Trump wants 350. Of course, Reagan had over 500."

Reagan was also in the 1980s, when we still had a lot of small tenders and escort ships in the Navy, I reminded him.

"Right. Of course a ship back then didn't have the fighting capability we have today," Ruttenbur agreed.

"I cover Huntington Ingalls (Industries), they are building the Littoral Combat ships. You park one of them out by a third-world country, you have 2,500 Marines ready to take over.  Our ability to deliver anywhere in the world has so (increased) from the '80s."

So what's the difference between the McCain and Trump budgets? "It's fighting over how much maintenance, how much retrofit," Ruttenbur said.  

Either way, won't a big military mean a lot more military recruitment -- and higher pay for our volunteer forces? "You will need more people," Ruttenbur affirmed. "They are talking about adding 50,000 Marines. There will be a lot more Army and Air Force." And those 70 additional Navy ships. "You will see a re-build-up of a volunteer military."

And war? Reagan re-armed but there was no new world war, the analyst reminded me,

Just a lot of smaller wars, or maybe the long war that doesn't end.