Washington (CNN) A decision by President Donald Trump to use force in retaliation for an alleged chemical weapons attack in Syria appears inevitable and imminent. But his goals in taking such action are less clear, as is the scale of the US response.

Trump effectively boxed himself into acting since he placed his and America's credibility on the line by blasting a Syrian government airfield with cruise missiles following a similar outrage against civilians last year.

The President vowed Monday to respond to a suspected chemical gas attack in Syria, saying the US response would be forceful.

"It will be met and it will be met forcefully," Trump said during a meeting with military leadership.

"We're going to make a decision tonight or very shortly thereafter," he said. "We can't let atrocities like we all witnessed ... we can't let that happen. In our world we can't let that happen."

It is now clear that Trump's flexing of presidential muscle last year did not deter Syria from the further use of such weapons, which Trump described as posing a major national security threat to the United States. So any new US strike would logically have to be more punitive and cause more damage.

"Another pinprick military strike is not going to really have too much effect, other than reinforcing the norm against chemical weapons use," said Kelly Magsamen, a former Obama administration national security official, on CNN. "I think the response is going to have to be slightly larger."

'Big price'

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By warning Sunday in a tweet that those responsible for the chemical weapons outrage would pay a "big price," the President has left himself with no room to take American forces in the region off high alert without firing their weapons.

But that doesn't mean Trump's decision on what to do next is a simple one. He must consider the multiple political and geopolitical consequences of using force.

Would, for instance, US strikes be confined to an attempt to punish local Syrian units or government officials deemed responsible for ordering the attack? Then, new national security adviser John Bolton and his team must consider whether the overarching goal is to reinforce US presidential prestige and the idea that Washington enforces red lines -- and if so how much force is appropriate to send that message.

If any US attacks went off track, Trump would have to explain to the American people why the use of force was necessary.

A decision to significantly increase the magnitude of US action would beg the question of whether Washington is trying to impose serious costs on the government of President Bashar al-Assad, who on Monday was branded a "monster" by Nikki Haley, the US envoy to the United Nations.

That scenario would involve a series escalation of the conflict and beg the question of what happens if Assad defies the US and continues to use chemical weapons. An escalating cycle of US action and Syrian countermoves could trap Trump in a slide into deeper involvement in the shattered Middle Eastern nation less than two weeks after he said he wants to bring US troops home.

Were the Syrian government the only power broker in its own country, the challenge would be complicated but one-dimensional. But Syria's fate is largely being dictated by US adversaries Russia and Iran, which propped up Assad at a pivotal moment in the civil war and are effectively waging a proxy conflict in the country that also includes Turkey and the United States.

By taking significant military action, perhaps over multiple days, Trump could send a signal of US resolve to Moscow and Tehran -- but would at the same time risk spiking tensions to dangerous levels.

Russian role

Former Obama administration national security adviser Tom Donilon suggested Monday that it was time to make Moscow pay a price for its role, possibly by targeting Syria's Russian-built air defense system.

"At some point you need to take a stand here. Russian behavior has been terrible," Donilon told CNN's Wolf Blitzer, while also calling for more sanctions on Russia and the creation of some kind of hybrid public tribunal to expose the culpability of Moscow and Assad in war crimes.

Still, there are risks to robust US action.

After all, around 2,000 US troops are in Syria fighting ISIS and many more are in Iraq, leaving them vulnerable to any reprisals by Iran especially.

The White House will also have to consider whether Russian forces on the ground in Syria should be warned of any impending attacks to avoid any casualties that could send Moscow-Washington tensions to the boiling point.

Trump could spread some risk by involving allies in any reprisal attacks, and there are signs that both Britain and France are ready to sign on.

Such a move would also strengthen the diplomatic impact of the punch and perhaps insulate Trump from any claims that he is acting to divert attention from worsening political and legal woes at home.

One intriguing aspect of the administration's response to the suspected chemical weapons assault has been signs of increasing impatience with Russia -- even from the President himself, who took the rare step of criticizing Russian President Vladimir Putin.

Defense Secretary James Mattis made an attempt to saddle Moscow with indirect responsibility for the attack.

"The first thing we have to look at is why are chemical weapons still being used at all, when Russia was the framework guarantor of removing all chemical weapons?" Mattis asked on Monday.

Haley's strong rebuke

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At the United Nations, US Ambassador Nikki Haley rebuked Moscow , which had branded pictures of the alleged chemical attack a "hoax."

"Russia could stop this senseless slaughter, if it wanted, but it stands with the Assad regime and supports it without hesitation," Haley said.

"Pictures of dead children mean little to governments like Russia who expend their own resources to prop up Assad," Haley said, condemning Russia's blocking efforts at the UN to push for a ceasefire in Syria.

Haley has a reputation for strong language and has been given considerable freedom at the UN to speak her mind. But it's possible that her speech in the Security Council represented an important turning point on Russia policy.

After all, when Trump tweeted, "President Putin, Russia and Iran are responsible for backing Animal Assad," he was singling out the Russian strongman for personal criticism in a way he has never done before.

Perhaps, after months of being solicitous to Putin and trying to forge a relationship with him at considerable political risk, Trump is losing patience.

David Lesch, author of the book "Syria, the Fall of the House of Assad" said Trump may blame Russia and its failure to control Assad for forcing him to plunge deeper into a conflict he wants to leave.

"I think Trump is really very angry with Russia, having named Putin in his tweets and comments," Lesch told CNN's Brooke Baldwin. "I think the anger and his exasperation in him is very real, inasmuch as he wants to get out of Syria, he keeps getting pulled back in."