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EVERETT, Wash. — Hillary Clinton portrayed herself on Tuesday as the only presidential candidate who has presented a detailed plan to defeat the Islamic State, which took responsibility for the terrorist attacks in Brussels earlier in the day.

“I’ve laid out a very specific agenda for defeating ISIS, not just on the battlefield,” Mrs. Clinton said at an event with union members here. She went on to explain her plan to use Kurdish and Arab forces and American airstrikes to weaken the group in Syria and Iraq, stem the flow of foreign funds used to arm the group, and increase efforts to stop recruitment online.

“We’ve got to defeat them online,” Mrs. Clinton said. “That is where they radicalize and that’s where they propagandize.”

Campaigning in Washington ahead of the state’s caucuses on Saturday, Mrs. Clinton used the events in Europe to question the readiness of her Republican rivals and, in particular, the leading Republican candidate, Donald J. Trump. “I see the challenge ahead as one where we’re bringing the world together, where we are leading the world against these terrorist networks,” she said. “Where some of my opponents want to build walls and shut the world off.”

“Well, you tell me,” Mrs. Clinton said in an obvious reference to Mr. Trump’s promise to build a wall on the Mexican border. “How high does the wall have to be to keep the Internet out?”

In the outskirts of Seattle, home to Amazon and Microsoft, Mrs. Clinton called on “our great tech companies to be helping us” in the fight against ISIS. On Wednesday, she is scheduled to deliver a speech on counter-terrorism at Stanford University, including her plans to defeat the Islamic State, her campaign said on Tuesday.

After Senator Ted Cruz of Texas outraged some American Muslims earlier in the day when he said that the terrorist attacks in Brussels called for American officials to “patrol and secure Muslim neighborhoods,” Mrs. Clinton struck an opposite note, calling for American Muslims to be a part of the fight to help the F.B.I. and law enforcement root out extremists.

“I want them to feel like they are part of our defense,” she said. “Not that they’re being insulted and isolated and left out.”

“Leadership isn’t about fanning those fears and that anger,” Mrs. Clinton concluded. “Leadership is saying we can do this together, because if we’re in a state of fear, we turn on each other.”