WASHINGTON (AP) — President Barack Obama is poised to become the first U.S. leader in three decades to attack a foreign nation without mustering broad international support or acting in direct defense of Americans.

Not since 1983, when President Ronald Reagan ordered an invasion of the Caribbean island of Grenada, has the U.S. been so alone in pursing major lethal military action beyond a few attacks responding to strikes or threats against its citizens.

It’s a policy turnabout for Obama, a Democrat who took office promising to limit U.S. military intervention and, as a candidate, said the president “does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation.”

But over the last year Obama has warned Syrian President Bashar Assad that his government’s use of chemical weapons in its two-year civil war would be a “red line” that would provoke a strong U.S. response.

So far, only France has indicated it would join a U.S. strike on Syria.

Without widespread backing from allies, “the nature of the threat to the American national security has to be very, very clear,” said retired Army Brig. Gen. Charles Brower, an international studies professor at Virginia Military Institute in Lexington, Va.

“It’s the urgency of that threat that would justify the exploitation of that power as commander in chief — you have to make a very, very strong case for the clear and gathering danger argument to be able to go so aggressively,” Brower said Friday.

Obama is expected to launch what officials have described as a limited strike — probably with Tomahawk cruise missiles — against Assad’s forces.

Two days after the suspected chemicals weapons attack in Damascus suburbs, Obama told CNN, “If the U.S. goes in and attacks another country without a U.N. mandate and without clear evidence that can be presented, then there are questions in terms of whether international law supports it; do we have the coalition to make it work?” He said: “Those are considerations that we have to take into account.”

Lawmakers briefed on the plans have indicated an attack is all but certain. And Obama advisers said the president was prepared to strike unilaterally, though France has said it is ready to commit forces to an operation in Syria because the use of chemical weapons cannot go unpunished.

The U.S. does not have United Nations support to strike Syria, and U.N. Secretary-General Ban Ki-moon has urged restraint. “Diplomacy should be given a chance and peace given a chance,” he said Thursday.

Expected support from Britain, a key ally, evaporated as Parliament rejected a vote Thursday endorsing military action in Syria. And diplomats with the 22-nation Arab League said the organization does not support military action without U.N. consent, an action that Russia would almost certainly block. The diplomats spoke anonymously because of rules preventing them from being identified.

“Presidents always need to be prepared to go at it alone,” said Rudy deLeon, who was a senior Defense Department official in the Clinton administration.

“The uninhibited use of the chemical weapons is out there, and that’s a real problem,” said deLeon, now senior vice president of security and international policy at the liberal-leaning Center for American Progress in Washington. “It can’t be ignored, and it certainly creates a dilemma. I think (Obama) had to make the red-line comment, and so Syria has acted in a very irresponsible way.”

The nearly nine-year war in Iraq that began in 2003, which Obama termed “dumb” because it was based on false intelligence, has encouraged global skittishness about Western military intervention in the Mideast. “There’s no doubt that the intelligence on Iraq is still on everybody’s mind,” deLeon said.

Both Republican George H.W. Bush and Democrat Bill Clinton had U.N. approval for nearly all of their attacks on Iraq years earlier. Even in the 2003 invasion, which was ordered by Republican George W. Bush, 48 nations supported the military campaign as a so-called coalition of the willing. Four nations — the U.S., Britain, Australia and Poland — participated in the invasion.

The U.S. has relied on NATO at least three times to give it broad foreign support for military missions: in bombarding Bosnia in 1994 and 1995, attacking Kosovo with airstrikes in 1999 and invading Afghanistan in 2001.

Only a few times has the U.S. acted unilaterally — and only then to respond to attacks or direct threats against Americans.

In 1986, Reagan joined ordered airstrikes on Libya to punish then-leader Moammar Gadhafi for the bombing of a Berlin dance club that killed two U.S soldiers and wounded 79 other Americans.

Three years later, George H.W. Bush invaded Panama after dictator Manuel Noriega declared war on the U.S. when his drug-trafficking regime was slapped with crippling American sanctions. The invasion began four days after a U.S. Marine was killed in a shooting in Panama City.

Clinton ordered a missile strike against Iraq in 1993 as payback for an assassination plot against the elder Bush. And in 1998, Clinton attacked al-Qaida bases in Sudan and Afghanistan to retaliate against U.S. Embassy bombings in Kenya and Tanzania that killed more than 200 people.

Obama approved the 2011 raid that killed Osama bin Laden, who had been considered a threat potentially going back to the 1996 bombing of the Khobar Towers in Saudi Arabia that killed 19 U.S. troops living there. Additionally, the U.S. has launched hundreds of deadly drone strikes on suspected al-Qaida havens, mostly in Pakistan, Afghanistan and Yemen during the presidencies of Obama and George W. Bush.

All other major U.S. military attacks since the 1983 Grenada invasion have been sanctioned by the United Nations. That includes the 2011 missile strikes that Obama ordered against Libya as part of a coalition to protect that nation’s citizens by enforcing a no-fly zone against Gadhafi forces.

Even the Grenada invasion had some international support. Six Caribbean island countries asked for U.S. intervention, which the Reagan administration said was legal under the charter of the Organization of American States. But the invasion was roundly criticized by Britain, Canada and the U.N.

Making the case Friday for the strikes, Secretary of State John Kerry noted that Turkey, France and Australia have condemned the suspected chemical attacks and said “we are not alone in our will to do something about it and to act.”

“As previous storms in history have gathered, when unspeakable crimes were within our power to stop them, we have been warned against the temptations of looking the other way,” Kerry said. “History is full of leaders who have warned against inaction, indifference and especially against silence when it mattered most.”

He added: “It matters here if nothing is done. It matters if the world speaks out in condemnation and then nothing happens.”

Some lawmakers in Obama’s party hedged in supporting an attack with little foreign backup.

“The impact of such a strike would be weakened if it does not have the participation and support of a large number of nations, including Arab nations,” Senate Armed Services chairman Carl Levin, a Democrat, said Friday.