World Bulletin / News Desk

Donald Trump and Hillary Clinton were plunged into questions about US national security Monday after three attacks in a single day put the threat of terrorism at the top of the US agenda.

Neither candidate has benefitted markedly from national security issues so far, judging from the reactions that followed June's attack on an Orlando nightclub or the string of attacks in Europe.

Republican Trump, who has made anxieties over security a cornerstone of his platform, lost no time in jumping on the latest events, speculating they could signal "a big change" with more attacks in the offing.

"Our country has been weak. We're letting people in by the thousands and tens of thousands. I've been saying you've got to stop it," he said on "Fox and Friends".

The billionaire has blamed the rise of the Islamic State group on Barack Obama and on Clinton, the former secretary of state and Democratic presidential nominee.

Trump advocates selectively closing US borders to people based on their country of origin, including barring the entrance of Syrian refugees. Trump has criticized Democrat Clinton's plan to allow more refugees from war-torn Syria into the US.

The real estate mogul opened a rally in Colorado Springs Sunday with news that "a bomb went off in New York" -- before local authorities had confirmed details of the explosion.

"I must tell you that just before I got off the plane, a bomb went off in New York and nobody knows exactly what's going on but, boy, we are really in a time," he told his supporters. "We better get very tough, folks. We better get very tough. We’ll find out."

"It's a terrible thing that's going on in our world and in our country and we are going to get tough and smart and vigilant."

Trump has boasted of his endorsements from the main organization representing US Border Patrol Agents and the nation's largest police union, as well as from more than 160 former generals and admirals.