In a policy speech, Trump said he would wage a multi-front "military, cyber and financial" war against Islamic State, although it was not clear how that would differ from the Obama administration's fight with the jihadist group.

"We will also work closely with NATO on this new mission," said Trump, whose remarks about the defense organization earlier this summer drew heavy criticism from allies and even some of his fellow Republicans.

Trump said a newly adopted approach to fighting terrorism by the organization had led him to change his mind and he no longer considered NATO obsolete.  He was apparently referring to reports the alliance is moving toward creating an intelligence post in a bid to improve information sharing.

While Trump appeared to claim credit for prodding NATO to focus more on the threat of terrorism, the 28-nation alliance has been grappling with the issue for more than a decade.  NATO invoked Article 5, its collective self-defense mechanism, for the first time in its history to offer support to the United States after the September 11, 2001, attacks.

Trump called for shutting down access to the internet and social media for those aligned with Islamic State, which holds territory in Syria and Iraq. But he said he did not want to detail military strategy because it would tip off potential foes.

"We will defeat radical Islamic terrorism just as we have defeated every threat we've faced at every age and before," Trump said, blaming his Democratic rival, Hillary Clinton, the former secretary of state, and President Barack Obama for aiding the rise of Islamic State.  In a speech in the swing state of Ohio, Trump also said that in implementing his call for a temporary ban on Muslims immigrating to the country, he would institute and develop a new screening test to try to catch people who intend to do harm to the United States.

As president, he said, he would ask the U.S. State Department and Department of Homeland Security to identify regions of the world that remain hostile to the United States and where normal screening might not be sufficient to catch those who pose a threat.

The Clinton campaign said Trump's plan to have immigrants submit to ideological tests was "a cynical ploy to escape scrutiny of his outrageous proposal to ban an entire religion from our country and no one should fall for it."

Reading from a teleprompter, Trump said Clinton did not have the judgment and character to lead the country. "Importantly, she also lacks the mental and physical stamina to take on ISIS and all of the many adversaries we face," he said.

Trump, a wealthy New York businessman whose volatile campaign has alienated some in the Republican establishment, faced a fresh rebuke on Monday as he falls behind Clinton in opinion polls ahead of the Nov. 8 election.  The Wall Street Journal, a leading conservative voice, said in an editorial he should fix his campaign within weeks or step down. Echoing growing alarm about Trump's candidacy among many leading Republicans, the newspaper said Trump had failed to establish a competent campaign operation.

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