Here’s where having someone with Mattis’s credibility in charge at Defense means everything to Trump politically. With him overseeing this, the proposal becomes a nervous “well, let’s wait and see what the plan is” thing for skeptics. With a random Trump crony in charge, it’s a “LIGHT EVERYTHING ON FIRE” moment.

The Defense Department is considering proposing sending conventional ground combat forces into northern Syria for the first time as part of an effort to speed up the fight against ISIS, CNN has learned.

“It’s possible that you may see conventional forces hit the ground in Syria for some period of time,” one defense official told CNN. But the official emphasized that any decision is ultimately up to the President. President Donald Trump has ordered his defense secretary to come up with a proposal to combat ISIS before the end of the month…

Conventional units operate in larger numbers and would require a more significant footprint of security protection both on the ground and in the air.

This is where I remind you that, contrary to Trump’s reputation as an isolationist and the conventional wisdom that the American public is war-weary, both have expressed support in the past for sending ground troops to Syria. Trump estimated at a primary debate last March that 20-30,000 Americans might be needed, probably the single most hair-raising interventionist note he hit during his entire candidacy. Opinion polls are mixed but several within the past 18 months have showed modest majority support for sending in the U.S. military to meet ISIS on the ground. A CNN poll taken in December 2015 found 53 percent in favor of deploying troops “to Iraq or Syria” to fight ISIS; a Morning Consult poll taken last October got the same number (who either “strongly” or “somewhat” support the idea) for sending troops “to Iraq and Syria.” Other polls, however, have had support for sending combat troops below majority levels even as the public remains open to less risky measures, like imposing a no-fly zone or targeting ISIS from the air. The X factor is how the public’s view of Trump will inform its views of an adventure in Syria. Most polling right now has him below 50 percent in job approval. If skepticism about him bleeds into skepticism about the mission, support for the deployment could collapse quickly. And if things go sideways and Trump is forced to choose between withdrawal and escalating with more manpower, the effect on his and the GOP’s popularity could be flammable.

On the other hand, if the military were to deliver a hard blow that finally broke apart the shrinking caliphate, Trump and his party would benefit bigly. Instantly it’d give them something to run on in 2018 and 2020: However chaotic the White House may be, the message would go, the man gets results when it comes to stopping the bad guys. The unanswered question for now is what exactly U.S. troops would be doing in northern Syria. Would they lead the fight against ISIS — or would the Kurds lead it, with the Americans in place mainly to soothe Turkey by showing that there’s nothing to fear from Kurdish separatists? Before you answer, read this intriguing WaPo story from two weeks ago about the Obama administration having prepared a plan for the Kurds to try to take Raqqa, ISIS’s capital, with material support from the United States. The great risk to that operation was how Turkey would react, one key reason why the Trump White House ended up throwing the plan in the trash:

The Kurdish fighters who volunteered to help the Americans had ties to the Kurdistan Workers’ Party, or PKK, which the Turkish and U.S. governments considered a terrorist group.

In contrast to Obama, Turkish President Recep Tayyip Erdogan did not see the Islamic State as his country’s No. 1 threat. In private meetings with senior U.S. officials in 2014, Erdogan said the Kurds were his top concern and that removing Assad ranked second, according to U.S. and Turkish officials…

The Obama plan required U.S. forces to train the Kurds in using the new equipment and fighting in a densely packed city, but it lacked details about how many U.S. troops would be required and where the training would take place, the Trump administration official said. Trump officials said they were dismayed that there was no provision for coordinating operations with Russia and no clear political strategy for mollifying the Turks.

What happens if the Kurds are sent in and they get bogged down outside or inside Raqqa? Unclear — which is another reason why the Trump administration passed on the plan, although Joint Chiefs chairman Joe Dunford reportedly supports the idea of letting the Kurds lead the fight. Could it be, then, that American troops would be stationed in northern Syria not to try to take Raqqa themselves but to act as a sort of buffer between Turkey and the Kurds, guaranteeing Erdogan that a large armed Kurdish force won’t eye his borders? Here’s what CNN says today: “What their exact mission would be is not yet clear, but one goal of their their presence would be to help reassure Turkey that Kurdish forces are not posing a threat to Ankara’s interests.” That sounds like more of a training/peacekeeping mission than a combat mission, but again, as noted, there’s no telling what happens if the Kurds can’t achieve their goals against ISIS. With American troops right there, it’d be the easiest thing for Trump to send them into the fight as back-up.

Here’s then-candidate Trump musing about 20-30,000 troops last year.