If there's one thing America's misadventure in Iraq from 2003 to 2011 taught everyone, it is that things can go terribly wrong when the U.S. intervenes in a foreign environment with deep sectarian divisions, an ineffectual government, armed factions, and the general complexities of the Middle East.

So now, Barack Obama plans to step up U.S. involvement in Iraq with more airstrikes and an effort to strengthen and better organize Iraqi and Kurdish military forces, as well as some Syrian rebels. In his address to the nation Wednesday night, the president laid out a multi-point proposal for action. He also had an opportunity, which he chose not to take, to warn Americans of some of the specific ways his new intervention could go wrong. "Any time we take military action, there are risks involved, especially to the servicemen and women who carry out these missions," Obama said. But he did not elaborate or explain any of those risks.

Since the president decided not to talk about possible downsides, here are a few — not at all a definitive list — of the things that could go badly awry as U.S. military forces return to Iraq.

1: The Iraqi government doesn't get its act together

Obama's entire Iraq policy rests on the notion that the country will form a government that is truly inclusive. According to this line of thinking, if Sunnis, purged under former Prime Minister Nouri al-Maliki, are given a meaningful, proportionate role in the government, their support for radical groups like the Islamic State of Iraq and Syria will diminish. "I've insisted that additional U.S. action depended upon Iraqis forming an inclusive government, which they have now done in recent days," Obama said Wednesday night. "With a new Iraqi government in place, and following consultations with allies abroad and Congress at home, I can announce that America will lead a broad coalition to roll back this terrorist threat." Without the new government, there would be no new U.S. intervention.

But what if the Iraqi government turns out to be not as inclusive as the president hopes, at the same time that the U.S. military is deeply involved in the fight against the Islamic State? "One of [the dangers] is that the Iraqi government fails to come together in any meaningful way," Peter Wehner, a former Bush White House official, said in an email exchange. "It may be that the government comes together but the country does not. That is, the Shia-Sunni split is impossible to repair, at least at this moment. It may be that a new government is formed but the leader himself is weak, or too sectarian, or too incompetent to wage an effective war against ISIS. It may be that the president increases our commitment in Iraq, but (unlike George W. Bush with the surge) not enough. The danger is that having re-engaged in Iraq, we don't succeed."

The bottom line is that — by the president's own reasoning — if a genuinely inclusive government fails to materialize, the U.S. mission, no matter how far-reaching, will fail.

2: The ground war is a dud

Nobody believes the U.S. can defeat the Islamic State with air power alone. A real victory over the Islamic State, the thinking goes, will be won with a ground war, supported by a overwhelmingly American air campaign. Without U.S. combat troops, the war will be fought by non-American boots on the ground — mostly Kurds and the notoriously unreliable Iraqi army, as well as, in Syria, some of the opposition forces the president once mocked as ineffective. Together, their performance will determine the outcome of the fight.

"The ground campaign is what is going to defeat ISIS in the end," said retired Gen. Jack Keane, a former Army Vice Chief of Staff, on Fox News Wednesday night. "In that ground campaign, we are totally dependent on surrogate forces. Whether we can do this or not, nobody knows."

"His plan is predicated on more U.S. assistance to equip Iraqi and Kurdish ground forces, and Syrian rebels, to take the fight to ISIS," added William Inboden, a former top official on the Bush National Security Council, in response to an email question. "What if Iraqi and Kurdish forces fail to step up and suffer repeated defeats by ISIS? U.S. airpower alone almost certainly won't be sufficient to 'destroy' ISIS. If the Iraqi and Kurdish forces and Syrian rebels aren't up to the task, and ISIS continues to grow in strength, is Obama prepared to send in U.S. ground forces?"

3: We really do become the Shiite Air Force

One major concern about American intervention in the Iraqi mess is that, by joining the fight against the Sunnis in the Islamic State, the United States would effectively go to war on behalf of the Shiite side of the sectarian divide. Everyone agrees that would be a disaster. "This cannot be the United States being the air force for Shia militias or a Shia-on-Sunni Arab fight," retired Gen. David Petraeus said over the summer. "It has to be a fight of all of Iraq against extremists, who do happen to be Sunni Arabs."

Despite being an outcome that all Americans want to avoid, that could be exactly what happens. "We're already seeing reports where U.S. strikes against ISIS are having the effect of bailing out Iranian-backed Shiite terrorist groups," said Republican Rep. Ron DeSantis, who served in Iraq in 2007 and 2008. "When I was in Iraq, once al Qaeda in Iraq was defeated, the main military front was taking on the Mahdi Army, a terrorist organization. Now, you could be in a situation where we are essentially serving as an air force for Shiite terror groups."

4: We drive away our timid, reluctant allies

In his speech, the president said America's coalition partners have already started playing roles in the anti-Islamic State campaign. "Already, allies are flying planes with us over Iraq; sending arms and assistance to Iraqi Security Forces and the Syrian opposition; sharing intelligence; and providing billions of dollars in humanitarian aid," Obama said.

One can certainly argue about how broad the coalition is; it contains fewer nations than earlier allied coalitions in Iraq. And it's not clear how willing the allies are to take on hard jobs. "Some people will not be comfortable doing kinetic," Secretary of State John Kerry said recently, using the administration's word to describe military action. "We understand that. Or some people don't have the capacity to do kinetic. But everybody can do something."

One serious fear, though, is that Obama might quickly alienate coalition partners by stressing the strict limits of U.S. involvement. "I'm worried that the administration will miscalculate because they believe they can elicit better action from our partners by constantly threatening to do less," said Peter Feaver, another former Bush National Security Council official, in an interview Wednesday. "The administration believes that the way you get the others to do more is you make clear all the things the U.S. is not going to do. The evidence shows you get more from allies when you reassure them on what you will do."

5) The status-of-forces-agreement problem blows up

President Obama has always explained that the U.S. left Iraq entirely, instead of leaving a residual force of somewhere between 10,000 and 20,000 troops, because the Iraqis would not go along with a status-of-forces agreement defining the terms of the American presence in Iraq, including immunity for American troops and contractors. There is a lot of controversy about just who held what position, but that is Obama's story. Whatever the case, there is no such agreement in place today.

So what happens when the bombs fall, the rockets are fired, and people, including, inevitably, some innocents, are killed? "We appear to be ramping up without a status-of-forces agreement, without the immunity protections the administration said was necessary," said Feaver. "What's the scenario if there is a horrible collateral damage problem that triggers the immunity problem? Things like that happen in war. And one of the reasons the administration didn't stay behind is that they didn't think the immunity provisions were strong enough."

That is just a brief list of possible bad outcomes in Iraq. There are more. Now, it could be that all the risks are outweighed by the urgency of taking action against the Islamic State. But the Obama administration would better serve both the American people and itself if it leveled with the public about what could go wrong. Anyone who lived through the war beginning in 2003 knows events in that part of the world can take tragic turns. Better to acknowledge that now, rather than be forced to later.