Hillary Clinton participates in a forum in midtown Manhattan on Sept. 8. (Melina Mara/The Washington Post)

Iraq has long been an uncomfortable subject for Hillary Clinton. Her vote to authorize the war alienated progressives and arguably cost her the 2008 Democratic presidential nomination. And now it's even being used against her by Donald Trump (who falsely claims to have opposed the war).

So Clinton took a bold step Wednesday night when it comes to Iraq and neighboring Syria, where the battle against the Islamic State has been raging for 13 years.

"They are not going to get ground troops," she said at a prime-time NBC forum. "We are not putting ground troops into Iraq ever again. And we're not putting ground troops into Syria. We're going to defeat ISIS without committing American ground troops."

She said it four times. Clearly, this was a message she intended to deliver.

She elaborated in a news conference Thursday morning.

The first big problem with this premise is the fact that there are already arguably ground troops in Iraq and Syria. The second is that in recent months, generals have asked for even more. In other words: The potential need for a ramped-up effort is already evident, but Clinton is completely foreclosing that option in a way that doesn't allow for changing circumstances.

At the core of Clinton's promise is the definition of "ground troops." The Obama administration itself has notably changed its own verbiage when referring to troops serving in Iraq and Syria. Obama said repeatedly in 2013 that there would be no "boots on the ground" in Syria.

"I will not put American boots on the ground in Syria," he said in a televised address in September 2013.

By 2014, though, the administration slightly altered its promise, pledging that there would be no combat troops on the ground. And then the administration in 2015 announced a small number of special forces would indeed be put on the ground there.

It's also worth noting here that there are technically thousands of U.S. troops already on the ground in Iraq. The administration stresses that these troops are training the Iraqis and serving in advisory capacities — not combat troops — but they are on the ground.

So it's somewhat odd that Clinton is drawing the line at ground troops and not combat troops, as the administration does. Even the administration's pledge has been tested at times; it's not hard to see Clinton's also coming under scrutiny in the years ahead.

Circling back to that second reason Clinton might regret her promise Wednesday night, it's worth noting that commanders-in-chief generally try to avoid taking options off the table.

And you needn't look far in the rear view to see why. Whether or not you think Obama has technically made good on his promise to not put ground troops in Syria, he has clearly failed to keep his promises to close the Guantanamo Bay prison and to bring all American troops home from Afghanistan by the end of his presidency.

The Fix's Amber Phillips said it well last year:

There are a variety of reasons things haven't gone Obama's way — some arguably his making, others he had no control over. Congress and other countries blocked many transfers of prisoners from Guantanamo Bay (though critics of closing Guantanamo would say this was predictable); whether the withdrawal from Iraq helped the Islamic State is much debated; and Iraq and Afghanistan's political turmoil hasn't made it easy for the president to exit those two countries.

But the bottom line is that Obama's campaign promises, which sounded feasible enough at the time to those who agreed with his worldview and rewarded him for it, relied on too much he couldn't control. He stepped into office in 2009 with a grand strategy — in his words, "to lead this country in a new direction" — but much has conspired to keep America's Middle East policy focused on Iraq and Afghanistan.

In sum: The only expectation is the unexpected — especially when it comes to the Middle East and the Islamic State. Taking options off the table, as Obama has done and now Clinton is doing, is fraught both militarily and politically.

Clinton's promise appeared to make even a top military adviser of hers, retired U.S. Air Force Brig. Gen. John Douglass, squirm Thursday morning. Pressed on her pledge on NBC's "Today," Douglass tried to make the case that she hadn't actually "meant" to take any options off the table.

"You can look at that one way or another, and I don't think she meant to take an option off the table," he said. "I think she meant to say that her policy is that she is not going to go in at the scale that [George W.] Bush and others have done there in Iraq."

But that's not what Clinton said. Her language clearly took the option of ground troops — however you define that — off the table in both Iraq and Syria.

There is simply no other way to read her comments. She said the United States would "never again" put ground troops in Iraq. She didn't allow for changing circumstances. She sought to allay concerns about her own hawkishness by making a blanket promise about what she wouldn't do as commander in chief.

The wisdom of those words could indeed be tested in the years to come.