Speaking from Havana, President Obama addressed the terror attacks in Brussels. (Reuters)

The terrorist attacks in Brussels on Tuesday pose the worst kind of foreign policy dilemma for President Obama, pitting his instincts that he’s doing all he can to defeat the Islamic State against intense political pressure for him to do more.

Obama has been making the case for months that his strategy to defeat the Islamic State and protect Americans at home is slowly working. White House aides speak repeatedly of the 40 percent of the Islamic State’s territory taken back from the group in Iraq and the 20 percent wrested away in Syria. They cite the impact of more than 11,000 U.S. military airstrikes, which they say 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 spoke on the condition of anonymity to comment frankly.

The reality — as Obama learned in the aftermath of the attacks in Paris and San Bernardino, Calif. — is that impressive battlefield statistics and reasoned calls for restraint mean little in the climate of fear generated by terrorist strikes.

Belgium was left reeling after three attacks left at least 31 people dead and more than 200 injured March 22. The terror began unfolding during peak rush hour, and ended with at least one suspect still at large. (Deirdra O'Regan/The Washington Post)

Obama, speaking in Cuba on Tuesday, struck a familiar tone in the immediate aftermath of the Brussels attacks. He projected resolve, insisting that “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 terrorist group in perspective.

The fundamental problem for Obama is that he is convinced, on the basis of his experience in Iraq and Afghanistan, that intensifying the fight against the Islamic State with more American troops, more airstrikes and raids would be counterproductive.

The White House and Pentagon have studied options that would accelerate the timeline for major attacks designed to clear the Islamic State from its main strongholds of Raqqa in Syria and Mosul in Iraq. Such plans could include increasing the number of U.S. combat advisers, pushing them closer to the front lines and loosening combat rules designed to minimize 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 allies of the United States improve intelligence collection and sharing, as the United States did after the 9/11 attacks. Secretary of State John F. 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 U.S.-backed opposition groups.

The temporary halt to the fighting should allow all the groups in the messy, multi-sided war to focus on fighting the Islamic State instead of one another, 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.

After the bloodshed in Brussels, the president’s approach once again came under GOP attack. “President Obama looks and sounds so ridiculous making his speech in Cuba, especially in the shadows of Brussels,” Republican front-runner Donald Trump tweeted.

Sen. Ted Cruz (R-Tex.) said that the country did not need another lecture on “Islamophobia.”

“We need a commander in chief who does everything necessary to defeat the enemy,” he said.

Privately, Obama has worried that a large-scale terrorist attack in Europe or on U.S. 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 U.S. Special Operations forces to track and destroy the Islamic State cells involved in planning terrorist attacks in Europe and North America.

If that is not enough, Obama could choose to speed up plans to drive the Islamic State from its major havens. Defense Secretary Ashton B. Carter said in January that the Pentagon was “looking to step up the tempo in Iraq and Syria” and hoped to push the Islamic State out of Raqqa and Mosul before the end of the year.

A major offensive in 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 potentially put some American forces in greater danger. There are some signs that this already may be happening. Before he took questions in Cuba on Monday, Obama paused to express condolences in the death of a U.S. Marine killed by an Islamic State rocket strike at an American fire-support base about 70 miles southwest of Mosul. The deployment of Marines to the base had not been previously announced by the Pentagon.

“Do you take the risk to accelerate the Mosul campaign?” asked Michèle Flournoy, a former senior Pentagon official in the Obama administration and an adviser to Hillary Clinton’s presidential campaign. “That’s a legitimate question.”

Until now, Obama’s instincts have told him to avoid such moves, which he has cast as unnecessary and the beginning of a slide toward 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 Center for American Progress.

If Obama does not 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 terrorist attacks and one of the most bitter and divisive political campaigns in recent U.S. history.

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