Sen. Rick Santorum, who has been trailing his opponent for months, accused Democrat Bob Casey on Thursday of being unqualified for the Senate "at a very critical time in our nation's future."

In the first of a two-day series of speeches on national security, Santorum said Casey fails to recognize the growing number of worldwide threats.

"From everything I see, my opponent, Mr. Casey, is unready, unqualified for the office that he seeks at a very critical time in our nation's future," Santorum said in a speech at PRL Industries, a metal-castings supplier that counts the military among its customers.

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Santorum said the U.S. must pay attention to escalating security threats from countries such as Iran, Venezuela and North Korea.

"We will have to face this threat because our enemies are fully committed to our destruction," Santorum said. "They will not stop until they destroy us or we destroy them."

Casey campaign spokesman Larry Smar called Santorum's comments "more fear-mongering from a politician who is desperately behind in the polls."

"The people of Pennsylvania are smart enough to see through this," Smar said. "Rick Santorum said North Korea isn't a threat, because Kim Jong Il just wants to watch NBA basketball. He's the same Rick Santorum who compared the war in Iraq to 'The Lord of the Rings.' This isn't the person to take foreign policy advice from."

Santorum, the No. 3 Republican in the Senate, argued Thursday for the United States to maintain its commitment to fighting terrorism overseas and at home, and to reduce the country's dependence on foreign oil.

He referred to what he said were multiple forces trying to undermine the U.S. as the "gathering storm," the title of Winston Churchill's memoir about the causes of World War II.

Santorum quoted the opening passage, in which Churchill said English-speaking peoples "allowed the wicked to rearm."

The senator gave his 40-minute speech in the heart of Pennsylvania's conservative center.

"I believe in this community, as well as people throughout the central part of the state, understand this threat and are willing to listen to people who tell them the truth, as opposed to folks who want to just sleepwalk through this problem," he said.