The terror attacks in Brussels pose the worst kind of foreign policy dilemma for US President Barack Obama, pitting his instincts, which tell him that he's doing all he can to defeat Isis (Islamic State), against intense political pressure to do more.
Obama has been making the case for months that his strategy to defeat Isis and protect Americans at home is slowly working. White House aides speak repeatedly of the 40 per cent of Isis territory taken back from the group in Iraq and the 20 per cent wrested away in Syria. They cite the impact of more than 11,000 US military airstrikes, which have killed more than 10,000 front-line fighters.
More quietly they strike cautionary notes. "This may be the most complicated conflict of our generation," said a senior administration official, who was granted anonymity to speak frankly.
The reality - as Obama learned in the aftermath of the attacks in Paris and San Bernardino, California - is that impressive battlefield statistics and reasoned calls for restraint mean little in the climate of fear generated by terror strikes.
Obama in Cuba struck a familiar tone in the immediate aftermath of the Brussels attacks. He projected resolve, insisting "we can and will defeat those who threaten the safety and security of people all around the world".
But the brevity of his remarks and his eagerness to pivot quickly back to his prepared speech also made clear that he was determined to keep the threat posed by the terror group in perspective.
The fundamental problem for Obama is that he is convinced, based on his experience in Iraq and Afghanistan, that intensifying the fight against Isis with more American troops, more airstrikes and raids is counterproductive.
The White House and Pentagon have studied options that would accelerate the timeline for major attacks designed to clear Isis from its main strongholds of Raqqa in Syria and Mosul in Iraq. Such plans could include increasing the number of US combat advisers, pushing them closer to the front lines and loosening combat rules designed to minimise civilian casualties.
But Obama has rejected those options, arguing that if there are no Iraqi or Syrian forces to hold the seized territory and provide humanitarian assistance the gains will be short-lived, said senior Administration officials.
Instead of big military offensives, the president has opted for lower-profile measures, such as helping America's allies improve intelligence collection and sharing, as the United States did after the 9/11 attacks. Secretary of State John Kerry has logged hundreds of hours working with Russians and Iranians to negotiate a fragile and imperfect cessation of hostilities between the Syrian Government and opposition groups backed by the Untied States.
The temporary halt to the fighting should allow all the groups in the messy, multi-sided war to focus on fighting Isis instead of each other, said Administration officials.
At home, Obama has sought to project determination and restraint, rejecting calls from Republican presidential candidates to lift all limits on the air campaign or bar all Syrian refugees from entering the United States.
Following the strikes in Brussels, the president's approach once again came under GOP attack. "Brussels was a beautiful city, a beautiful place with zero crime. And now it's a disaster city," Donald Trump, the Republican front-runner, said on Fox News. "It's a total disaster, and we have to be very careful in the United States, we have to be very careful and very vigilant as to who we allow in this country."
Senator Ted Cruz said that the country didn't need another lecture on "Islamophobia". He added: "We need a commander in chief who does everything necessary to defeat the enemy."
Privately, Obama has been concerned that a large-scale terror attack in Europe or on American soil could force him to plunge American forces into another large and costly war in the Middle East - something he has vowed to avoid. In the near term, this nightmare scenario could lead Obama to deploy more US Special Operations forces to track and destroy the Isis cells involved in planning terror attacks in Europe and North America.
If that isn't enough, Obama could choose to speed up plans to drive Isis from its major havens. Defence Secretary Ashton Carter said in January that the Pentagon was "looking to step up the tempo in Iraq and Syria" and hoped to push Isis out of Raqqa and Mosul before the end of the year.
A major offensive into either of those cities in the near term would require a significant shift in the Administration's strategy, which relies heavily on local partners, and could put some American forces in greater danger. There are some signs that may already be happening. Before he took questions in Cuba on Tuesday, Obama paused to express condolences for a US Marine killed by a Isis rocket strike at an American fire support base about 110km southwest of Mosul. The deployment of Marines to the base hadn't been previously announced by the Pentagon.
"Do you take the risk to accelerate the Mosul campaign?" asked Michele Flournoy, a former senior Pentagon official in the Obama Administration and adviser to Hillary Clinton's presidential campaign. "That's a legitimate question."
Up until now, Obama's instincts have told him to avoid such moves, which he has cast as unnecessary and the beginning of a slide towards a much larger American commitment of forces. "I'd be deeply surprised if the President in his final months in office tore up his template in Iraq and Syria," said Brian Katulis, a Middle East expert at the left-leaning Centre for American Progress.
If Obama doesn't undertake a dramatic change in course, the biggest challenge for him will be finding the right tone to reassure the American people - something he struggled to do after the Paris and San Bernardino attacks.
"Every president has strengths and weaknesses," Obama said in a recent interview with the Atlantic. "And there is no doubt that there are times where I have not been attentive enough to feelings and emotions and politics in communicating what we're doing and how we're doing it."
The test for Obama is whether he can simultaneously communicate resolve and the need for restraint in Iraq and Syria amid new terror attacks and one of the most bitter and divisive political campaigns in recent history.