Ash Carter’s appointment as Secretary of Defense signals a significant departure by President Obama. Despite his three predecessors in the post having been people who had held a variety of distinguished public offices, none could really be regarded as “insiders” at the Pentagon. Carter has a wealth of experience working there over the last decade. It is one of the major points that suggests he will enjoy the confidence of his three key constituencies – the Joint Chiefs of Staff, the officials who will serve under him, and the President himself.

It remains to be seen whether that means Carter will be able to pierce the tight-knit group of foreign policy advisors of whom we have heard so much in the last week or so. Indeed, despite his pedigree, Carter does represent something of a risky appointment for the president.

That’s because Carter is reputedly a forthright person, a different mould from Chuck Hagel who was characterized in the press as a “team player” who was sidelined. A failure to heed Carter’s advice and sideline him raises the prospect of ignoble fight between Carter and the White House – one more thing the President doesn’t need at the moment.

Let’s assume that the president knows what he is getting in Ash Carter: one of the best educated and most bureaucratically informed people to hold the post in recent times. He is someone who formulates positions and then acts to implement them precipitously. Let’s also assume the president is prepared to avoid any public squabbles by giving Carter both independence and influence. What are the chances that Carter will be President Obama’s last, and most successful appointment as Secretary of Defense?

We’ve already covered most of the pros. Carter knows the job he coveted for a while and is an expert steeped in the foreign policy issues from both his time at the Pentagon and at Harvard’s renowned Belfer Center for Science and International Affairs. He has demonstrated managerial capabilities as the DoD’s Deputy Secretary and a reputation for a more aggressive position that will likely be closer to those of the Joint Chiefs who have been clamoring for a greater show of force against the Islamic State in Iraq and Syria. Finally he has a track record on key policy issues that is likely to find a solid block of support in his Congressional confirmation hearings from both Democrats and those Republics who eschew more isolationist policies such as Senator John McCain.

The cons, however, are formidable. The first is the context in which Carter finds himself. With the next presidential election less than two years way, he’ll have to accomplish significant organizational and policy changes in a hurry. The Pentagon is like a big ship; it takes time to institute a major shift in direction. The natural tendency towards bureaucratic inertia means Carter will have to tread on some significant toes. If successful, he might be held over by Obama’s successor, as was Robert Gates. But he can’t work on that assumption. A seven-year plan allows for patience. A two-year plan does not.

The second challenge is one that any appointee to the post faces: the changing nature of conflict. America’s military prowess was founded on the capacity of its forces to fight conventional wars against other states in the skies, on land and – most importantly – on the seas. That is no longer the case. We have developed a new lexicon to describe the kinds of wars we must fight nowadays: irregular wars against guerilla movements, notably Al-Qaeda as it hides in caves. Or hybrids wars that mix everything from insurgencies to cyber hacking.

Pentagon officials are fully cognizant of these changes. But fighting America’s enemies has become a lot more nuanced and the scope of its duties has vastly expanded. The US Navy has to patrol the seas for smugglers of fissile materials that might be used for a nuclear device in a suitcase or on a warhead. Its Coast Guard has to patrol America’s borders to stop the smuggling of drugs. And in space – and cyberspace – we need to prowl for information in the name of national security. The days of armies lined up against each other on a hillside are over. Any Secretary of Defense has to build or maintain a military force prepared to repel threats that his (or eventually her) predecessors could not have imagined - while still ensuring that the Russians will be sufficiently deterred from marching further into the Ukraine.

It is not an enviable task. It is hard to be a success under those circumstances. But it is one the new Secretary of Defense will have to face – while he hits the ground running.

Simon Reich does not work for, consult to, own shares in or receive funding from any company or organisation that would benefit from this article, and has no relevant affiliations.