A former adviser to Hillary Clinton on Syria, Frederic C. Hof, now a Resident Senior Fellow at the Atlantic Council's Rafik Hariri Center for the Middle East, has called for invading Syria in the wake of the deadly attacks in Brussels.

"For the better part of a year, one clear recommendation has been on the table: assemble an American-led, coalition-of-the-willing, professional ground component—one top-heavy in regional and European forces—to enter eastern Syria to close with and kill ISIS. Engaging the Syrian opposition at all levels, consistent with an executable civil-military stabilization plan, can produce an administrative structure for an ISIS-free eastern Syria. Killing ISIS in Syria can ease the migration crisis and hasten the demise of this murderous band in Iraq. And it can demonstrate to the credulously stupid that linking up with losers will be a one-way trip to self-destruction," Hof writes.

"Time is not the friend of the West on this issue," he continues. "The idea that Syria's Bashar al-Assad—a major enabler of ISIS—should step aside as a result of negotiations so that a united Syrian front can be formed to liberate eastern Syria is fine in theory. Russian and Iranian military operations in support of their Syrian client have all-but killed it in practice. Waiting for the barbarians—who recruit on the basis of their own survival and Assad's atrocities—to hit the American homeland and then retaliate with an all-American force is always an option. But why wait? Why make it all-American? Why not do the heavy, coalition-building diplomatic lift that has been recommended for months and kill these bloodthirsty criminals sooner rather than later?"