President Barack Obama once ridiculed a political opponent for suggesting the military should look to its past to determine how it should fight today.

Former Massachusetts Gov. Mitt Romney based his 2012 White House bid in part on strengthening some basic elements of the military, including building more ships. During the last debate of the campaign that October, the Republican repeated his criticism that the Navy was smaller than it was in 1916, setting up for his opponent what would become a notorious shut-down line.

“Well, governor, we also have fewer horses and bayonets, because the nature of our military has changed,” the incumbent retorted, explaining how the military’s shrinking size was offset by increased lethality through modern inventions like aircraft carriers and submarines. “The question is not a game of battleship, where we’re counting ships. It’s ‘What are our capabilities?’”

Obama’s argument that night was based on a warfighting doctrine he has embraced more than any modern president – emphasizing small, nimble and highly lethal forces and equipment in favor of the rumbling tank-borne armies that freed Europe from the Nazis, deterred the Soviets for half a century and marched on Iraq twice. But some of the country’s premier military minds are now forcing the president to think again about those tactics amid re-emerging threats that require a more conventional response.

Defense Secretary Ash Carter on Tuesday offered a preview of the nearly $600 billion defense budget Obama will unveil next week. And he admitted America’s warfighting effort is about to change.

His remarks followed the release of recommendations from a congressionally appointed commission formed to study the future of the U.S. Army that believes the military should look more to its past to determine how to get back on the offensive against Russia, North Korea, China or the Islamic State group.

In the new priorities Carter outlined, he promoted Russia and China to the top slots of America’s international concerns. And he called for new military deployments to Europe, effectively quadrupling its military budget there.

“To be clear, the U.S. military will fight very differently than we have in Iraq and Afghanistan, or in the rest of the world’s recent memory,” Carter said. “We will be prepared for a high-end enemy – that’s what we call full-spectrum. In our budget, our plans, our capabilities and our actions, we must demonstrate to potential foes that if they start a war, we have the capability to win.”

The problem? While the U.S. focused for years on large-scale counterinsurgency operations in the Middle East – operations that prompted the development and production of more nimble and responsive equipment, like mine-resistant troop vehicles known as MRAPs, handheld drones and other gear American forces have determined they needed to fight dusty, messy and indefinite wars in the streets of Iraq and the mountains of Afghanistan – the armies of America’s enemies evolved.

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Meanwhile, Russia embarked on a program to strengthen and improve its military. It invested in new highly advanced tanks, planes that can launch multiple missiles at once and deadly surface-to-air missiles like the S-400 it has since deployed to Syria. The hardware has been used in its ongoing campaigns to defend the Syrian regime of Bashar Assad, to protect the strategically critical Crimean peninsula it annexed in 2014 and to prop up separatist rebels in eastern Ukraine.

At the same time, the Islamic State group employed military maneuvers more akin to conventional war than any other extremist group the U.S. has faced, and combined it with insurgent tactics to flood across the border into Iraq, exploiting the Syrian civil war and the full U.S. withdrawal from Iraq in 2011 to solidify its so-called caliphate in Raqqa.

And China’s projecting military strength, including its creating islands to support its naval and air forces, affects stability in the region perhaps more than any other single factor in Asia.

The events caught the U.S. military-intelligence apparatus flat-footed.

Now the military under Carter’s watch has to find an answer. The National Commission on the Future of the Army last week released its final report with more than 60 recommendations. Among them is that the military should once again permanently base tanks in Europe to offset Russian aggression and a combat aviation brigade in South Korea for greater deterrence against its increasingly belligerent northern neighbor. It also pointed to a troubling absence of short-range air defense artillery in an army that hasn’t prioritized protecting itself against a foreign air force since the end of the Cold War but now operates in the same battle space where Syrian and Russian jets and bombers attack common targets in the Islamic State group. So the Army should also reassess those risks, the commission states.

Military officials are now faced with the task of rectifying these and dozens of other recommendations with the Pentagon’s own strategy, virulent political appetites on Capitol Hill, as well as the legacy of a two-term president who promised to usher in a new era of peace but will leave office with a U.S. presence in more war zones than when he was sworn in.

According to some defense officials, under Obama’s watch the military wasn’t ready for what it faces now.

“[In 2013], ‘Russia’ didn’t exist. ISIS wasn’t out there. Ebola – our commitments in Africa and lots of other places,” a defense official familiar with the work of the commission said before the report was released last week. “What we can say is that we’ve continued to see and experience a very high op-tempo in support of global requirements, and that’s putting a strain on the force.”

The Army’s top officer, Gen. Mark Milley, was asked in September about the balance between the “light” force the service branch has prioritized for its wars in Iraq and Syria versus the “heavy” units of tanks and artillery it favored in previous eras. He didn’t have an answer.

“There are some who are suggesting that perhaps we have lightened our force too much, lightened the Army too much over time, and others who have suggested that we've basically become a motorized or wheeled-vehicle-type army, and that we've actually lost our light capabilities, and there's fair arguments on all sides of that,” Milley, the Army’s chief of staff, said in a question-and-answer session after remarks to the National Guard Association.

“We don't have the luxury of fighting against a singular opponent in a singular piece of terrain or a singular area of responsibility,” he said. “We could end up fighting lots of different types of opponents in lots of varied types of terrain.”

He deferred to the commission’s work to inform how the Army will find the right balance, which has been a problem since World War II. Peacetime, for example, has seen a decrease in Army capability, forcing the government to overspend its budgets or exhaust its people to get it back up to fighting strength when a conflict emerges. The commission’s report refers to this as “the readiness crisis.”

“Peacetime savings always seem pennywise at the time,” it states. “But when wars come, policymakers and commanders struggle to build forces for the fight, often regretting not having made the Army ready before sending soldiers into combat without the formations, numbers, equipment, supplies, or training they need to accomplish the mission.”

The commission was led by a group of seasoned military and government officials picked by both the president and the chairmen and ranking members of the House and Senate Armed Services committees. Their charge was gargantuan: determine how the Army should change to become most effective for the price at a time when it was culling 150,000 soldiers from wartime highs and government budgets are slashed by planned military reductions and a continuation of the congressionally mandated across-the-board budget cuts known as sequestration.

One of their central tasks was to determine the extent to which the Army, Army Reserve and the National Guard should tear down institutional barriers and rely on one another more, as they have in the wars in Iraq and Afghanistan. (Many cargo and troop transport planes, for example, are operated by Air National Guard units). In doing so, they could ideally provide soldiers the career-long flexibility they seek to raise a family or go back to school to get the most out of their time in uniform, all while fulfilling the requirements for protecting the homeland.

Their work revealed what they consider troubling shortfalls in what the Army has become.

The commission’s recommendation to bolster the Army’s tank presence in Europe originated from what its members describe as a definite and severe lack in the Army’s combat armor capabilities, which pushed the commission to recommend permanently stationing an Armored Brigade Combat Team – tanks – in Europe, as well as the new aviation unit in South Korea.

In some ways, that kind of deployment seems outdated in 2016. The Army alone had more than 216,000 troops based in Europe in 1989, a presence that saw sharp declines amid the dissolution of the Soviet Union. Today, only 28,000 soldiers remain there.

The commission’s leaders, however, say the recommendations are anything but a return to the past.

“I don’t think it’s looking back,” said Carter Ham, a retired four-star Army general who finished a 39-year career of combat leadership in 2013 as the head of U.S. Africa Command. “I think it’s indicative of how rapidly the global security environment can change.”

“A couple of years ago, there was not a view that there would be much of a threat in Europe. That condition has changed,” he said, describing the complexities of the military’s modern decision-making process. “The challenge is, how do you manage that system without knowing that you’ll never be precisely right? You won’t ever be able to precisely predict the nature, time or place of the next conflict, but to generally be right and to be prepared for a host of contingencies.”

Fellow commission member Kathleen Hicks, a former senior defense official for policy at the Pentagon, now with the Center for Strategic and International Studies, agrees.

“We did not try to design a force that fought the Fulda Gap years ago,” she said, referring to the lowlands approaching Frankfurt where NATO planners believed Soviet tank commanders would attempt an invasion on West Germany. “That doesn’t mean there won’t be some continuities through time, and armor is still a piece of the picture in the future.”

The commission’s recommendations focus on how the U.S. should deter and, if necessary, defeat the Russians today, through their advanced employment of new technologies like space and cyber warfare, which Putin’s military has employed with great effect in Ukraine and Georgia. America’s resources should pour into equipment and tactics it can use to embolden friendly allies, the commission believes.

“The enablers – armor – is a key piece of that,” Hicks said. “The Russians do, unfortunately for us, have very advanced armor, and short-range air defenses was probably the biggest notable item where we saw incredible advances in Russian capability.”

Finding the money to station permanent tanks and troops to square off against the Russians shouldn’t be difficult, despite the austere financial environment surrounding the defense budget. But the problems likely won’t end there.

“Politically, there’s going to be fairly robust support,” said Katherine Blakeley, a defense budget analyst with the Center for Strategic and Budgetary Assessments. “But it’s finding the financial resources to support that – an alignment of strategic vision between the Obama administration, the Pentagon and Congress.

“It’s going to be something that ties very closely to the political fight about what to do about a perceived greater threat from Russia in the near term. And it’s going to tap very much into that debate.”

Carter included in his remarks Tuesday a catalogue of new technologies defense scientists have produced that are clearly aimed at deterring Russian or Chinese aggression. These new technologies include swarming drones, micro-drones that have already been tested to deploy from an aircraft traveling Mach 0.9, electromagnetic railguns, and self-propelled howitzers. The Pentagon will continue its work on developing the F-35 fifth-generation fighter jet (despite its developmental woes), fast-attack submarines and more smart bombs to kill Islamic State group fighters amid depleted stockpiles.

Completing these tasks requires addressing the complexity of threats today, he said.

“That kind of singular focus may have made sense when we were facing off against the Soviets or sending hundreds of thousands of troops to Iraq and Afghanistan, it won’t work in the world we live in today,” Carter said. “Now we have to think and do a lot of different things about a lot of different challenges – not just ISIL and other terrorist groups, but also other competitors like Russia and China, and threats like North Korea and Iran.”