The presidential campaign took another sharp turn toward national security Tuesday, as a deadly terrorist attack in Brussels prompted promises from the Republican and Democratic candidates that they would keep America safe if elected.  

In the hours following the attack — which authorities say killed more than 30 and injured nearly 200 others, according to the Associated Press   — the field of presidential contenders proposed a renewed military campaign against the Islamic State, also known as ISIS, and to tighten security at home. ISIS has claimed responsibility for the attack.  

It also exposed deep fissures in the race, not only between Republicans and Democrats, but between Donald Trump and his two remaining rivals for the nomination. Both Sen. Ted Cruz of Texas and Ohio Gov. John Kasich seized on Trump’s recent comments questioning America’s role in NATO in an attempt to paint him as soft on national security.  

But to Trump, the attacks were another opportunity to talk about the issue that has animated his campaign from the beginning: closing the country’s borders.  

“It’s going to get worse and worse, because we are foolish, we are foolish,” Donald Trump said during an interview on Fox News . “We can’t allow these people, at this point, to come into the U.S.”  

The country needs to “close up our borders,” he said.  

In an interview with NBC , Trump also renewed his approval of waterboarding, which critics contend is tantamount to torture.  

“Frankly, the waterboarding, if it was up to me, and if we changed the laws or had the laws, waterboarding would be fine,” Trump said. “If they could expand the laws, I would do a lot more than waterboarding. You have to get the information from these people.”  

Cruz called for tightening U.S. borders to visitors from abroad, as well as better monitoring of Muslim residents here.  “We need to immediately halt the flow of refugees from countries with a significant al Qaida or ISIS presence,” Cruz said in a release.” We need to empower law enforcement to patrol and secure Muslim neighborhoods before they become radicalized.”  

The rise of the Islamic State, terrorist attacks in Paris and San Bernardino, Calif., and now Tuesday’s deadly bombing of a Brussels airport and metro station have thrust national security into the spotlight. Polls show that many voters, especially Republicans, now consider it one of the top issues in the campaign.  

Republicans have used the public’s growing concern to attack President Barack Obama, whose efforts to lessen America’s footprint abroad, they say, has made the world a more dangerous place.  

In a tweet, Kasich called on Obama to end his trip to Cuba immediately to return to Washington.  

“The president must return home immediately and get to work with our allies to respond with strength against the enemies of the west,” he said.  

But Republicans also trained their fire on Trump. His chief rival for the nomination, Cruz, called for NATO to begin a military campaign to destroy the Islamic State.  

“It is striking that the day after Donald Trump called for weakening NATO, withdrawing from NATO, we see Brussels,” Cruz said, noting that it is the host of the headquarters of the alliance.  

Trump had said that the U.S. needed to rethink its involvement in the organization because of the amount of the U.S. contribution and ways in which the world has changed since the founding of NATO, which was established against the treat posed by the Soviet Union.  

“We are paying disproportionately. It’s too much, and frankly it’s a different world than it was when we originally conceived of the idea,” Trump said.  

The Democratic front-runner, Hillary Clinton, rejected calls to close the border.  

“We need to do much more to tighten things up,” she said during an interview on NBC. “I know our security professionals are working to do that. It’s unrealistic to say we’ll completely shut down our borders to everyone.”  

But she added that “we have to intensify efforts to keep America safe.”  

“Americans have every reason to be frightened about what they see,” she said.  

Gillian Roberts contributed to this st ory  

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