"It goes without saying that when you have attacks that take place, when 30 people get killed in Brussels, something went wrong ... We have got to improve our efforts to make sure it does not happen again," he told CNN's Jake Tapper on "State of the Union" Sunday when pressed for specifics.
Sanders credited President Barack Obama for his handling of the fight against ISIS, saying that the terrorist organization is "on the defensive. They are retreating."
Sanders also made a claim that seems at odds with intelligence agencies' concerns about ISIS-inspired attacks in Western countries.
"I think we know who ISIS is. We know those people who are planning attacks against our European allies and against ourselves," he said.
Sanders' comments come after he swept three Western Democratic presidential caucuses on Saturday, defeating Hillary Clinton in Washington, Alaska and Hawaii.
Of his campaign, which lags behind Clinton in the delegate count in large part because Clinton has been endorsed by many more so-called "superdelegates," Sanders said that "we think we do have a path to victory."
He admitted he'd been drubbed by Clinton in the South, but said the race is now shifting to the coastal states, among the nation's most liberal.
"We've won the last five out of six contests, all of them in landslide victories," he said, referring also to wins in Utah and Idaho last week, while Clinton won Arizona.
Sanders said his campaign plans to push superdelegates to back off their endorsements of Clinton.
"I think when they begin to look at the reality, and that is that we in poll after poll are beating Donald Trump by much larger margins than is Secretary Clinton ... A lot of these superdelegates may rethink their position for Secretary Clinton. A lot of them have not yet declared," he said.
He also predicted those superdelegates will fall under pressure to support the winners of their states and congressional districts.
"I think their people are going to say to them, look, why don't you support the people of our state, vote Bernie Sanders," Sanders said.
The Vermont senator also kept up his attack on Clinton for her attending a fundraiser hosted by George and Amal Clooney, with a price tag of more than $353,000 per couple to sit at the head table.
The problem, Sanders said, is "not Clooney, it's the people coming to this event."
"I have a lot of respect for George Clooney. He's a great actor. I like him. But this is the problem with American politics, is that big money is dominating our political system," Sanders said.
He said his campaign's events, even with big-name headliners, usually cost "$15 or $50" to get into.
"So it's not a criticism of Clooney," he said. "It's a criticism of a corrupt campaign finance system, where big money interests -- and it's not Clooney, it's the people coming to this event -- have undue influence on the political process."