Making New Year’s predictions is tricky in this turbulent world, but here’s one fairly safe bet: The next president will propose a more assertive U.S. foreign policy. Hillary Clinton, the likely Democratic nominee, has often sounded nearly as hawkish about use of military force as the Republican contenders.

But what would a new American assertiveness mean, in practical terms? What can U.S. military power do, realistically, to combat the Islamic State and other threats more effectively? How can China and Russia be checked militarily? The rhetoric of American power will be flexed during the campaign, but what about the substance? Projecting power will be harder than many candidates seem to realize.

The first reality check for a new president will be the Pentagon. This generation of military leaders has been through traumatic wars in Iraq and Afghanistan. They’ve cautioned President Obama about the potential cost in lives and money of new commitments in the Middle East, and they’ll do the same with the next commander in chief. If you want to hear arguments against deploying a big U.S. ground force in Syria, just ask a general.

Half-baked ideas about projecting power aren’t likely to survive long in a new administration. There will be continuity in military advice, given that Gen. Joe Dunford and Gen. Paul Selva likely will remain into 2017 as chairman and vice chairman of the Joint Chiefs of Staff, respectively. A new roster of combatant commanders, including the CENTCOM chief who will oversee the Middle East, will be appointed by Obama before he leaves office.

My guess is that before Obama departs, he will adopt some of the more aggressive military options he has been resisting, such as “safe zones” inside Syria and more aggressive deployment of U.S. special forces. That’s partly because the U.S. is likely to face more jihadist-inspired terror attacks in 2016 — increasing public pressure on the president to retaliate. A weak White House response, among other things, would undermine the Democratic candidate’s chances.

If the U.S. may be compelled by circumstances to escalate its tactics against the Islamic State, there’s an argument for doing so sooner rather than later — so as to maintain better control of American military actions and not be forced by a panicky public into overreaction. The next president will also want to control options after the inauguration rather than be a prisoner of events — adding to the likelihood of early requests to the Pentagon for new military options.

The Middle East will remain a military muddle for the next president, as it has so often been for the last two. But in dealing with China and Russia, the next administration will have clearer choices about projecting military power. The next White House will also face less resistance on these fronts from military commanders, who are well-schooled in the Russian and Chinese threats and believe they have the military tools needed to confront them.

To contain Russia, the next administration will probably examine whether to deploy U.S. forces in Eastern Europe, as a tripwire against Moscow’s aggression. That move would likely have Pentagon support. The military would also welcome more active moves to contain China’s actions in the South China Sea, including closer cooperation with allies such as Japan and the Philippines, which are bolstering their own defenses.

The trickiest military questions for the next president will involve what strategist Michael Mazarr calls “gray-zone conflicts.” In a recent article published by the U.S. Army War College, Mazarr argues that China, Russia and Iran have been using these “gray” strategies to frustrate U.S. goals without openly committing military force.

U.S. adversaries exploit power gaps. It’s easier for Russia to invade Ukraine with irregular forces out of uniform, the so-called “little green men,” than to send a conventional army that would challenge NATO. It’s easier for China to assert its maritime power by creating artificial islands in the South China Sea than by defying the U.S. Pacific Fleet with an aircraft carrier. It’s easier for Iran to send Lebanese and Iraqi Shiite militias to Syria than to commit its own military directly.

The Pentagon mostly buys weapons for black-and-white conflicts, rather than gray ones. So it isn’t well-prepared for such “hybrid” approaches.

Campaign rhetoric about more military spending and a tougher defense posture could deepen this problem — if it simply leads the next president to bolster existing forces. A genuinely assertive strategy would create new tools that can function better in the gray of future conflict.

David Ignatius’ email address is davidignatius@washpost.com.