Republican presidential candidate Scott Walker is calling for U.S. forces in Iraq to engage in direct combat to defeat "radical Islamic terrorists" in the Middle East.

Yet even as the Wisconsin governor predicts a "generational struggle," he continues to avoid calling for additional ground troops beyond the roughly 3,200 military security personnel, trainers and advisers now deployed. The Islamic State is believed to have up to 30,000 fighters with replacements coming in as fast as the current U.S.-led coalition and Iraqi forces can kill them.

Walker outlined his foreign policy vision Friday at The Citadel, a military college in the early voting state of South Carolina.

"The administration is tying up our troops with political restrictions, preventing them from doing what is necessary to defeat ISIS," Walker said. "These restrictions must be lifted immediately and all other options should remain on the table."

But, he said, the effort "must be part of a broader, U.S.-led, regional coalition, with real buy-in and ironclad guarantees from our allies that they will help us shoulder the burden."

Walker delivered his 3,000-word address in front of several hundred Citadel cadets, telling them they "will be part of the fight."

"I will send you into battle when, and only when, our national security is at risk, and I will send you with a plan for victory," Walker said.

Walker did not say what the U.S. would do if the Islamic State was defeated.

Earlier this week at a campaign stop, he offered an explanation.

"My goal, my intention, is not to send new troops in," he said. "It's to first unleash the power, lift the political restrictions, see how far that goes and then use military decisions, not political or bureaucratic decisions to determine what role we should play."

Besides fighting enemies overseas, Walker said his plan to, "keep our children and grandchildren safe from the threat of radical Islamic terrorism" also requires securing the U.S.-Mexico border; bolstering counterterrorism and surveillance programs; and using economic sanctions to cut off financial capabilities in Syria and Iran.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, has cautioned against thinking that defeating IS and the broader problem of violent Islamic extremism is as simple as having U.S. troops take control of the fight in Iraq. Without estimating how many U.S. troops it might take, he has said the U.S. could defeat IS, but said the victory would be short-lived absent an Iraqi government supported by Sunni Muslims as well as Shiites and Kurds.

Stephen Biddle, a professor of international affairs at George Washington University and a sometime-adviser to U.S. war commanders, said it might take a large number of U.S. troops to defeat IS in Iraq and Syria. "No, I don't think a brigade would be enough," he said, referring to an Army unit numbering about 3,500 soldiers.

"You'll remember that we had north of 100,000 troops there in 2006 and it wasn't enough. Moreover, the Iraqi state military today is no better than it was in 2006. It's arguably worse.

"There are a lot of arguments out there at the moment that posit hope that a relatively modest escalation will enable us to destroy ISIL, whether in Iraq or overall," Biddle said, using an alternate acronym for Islamic State. "And I just think there is very little basis for that view in actual experience."

The speech comes as Walker is trying to bolster his image as a ready commander-in-chief. Earlier this week, he called on President Barack Obama to cancel an upcoming state visit with Chinese President Xi Jinping. Walker maintains that Obama should punish China for alleged currency manipulation and human rights abuses, though he has not detailed how a Walker administration would settle differences with China without face-to-face meetings.

Walker used the address to cast Obama and Democratic presidential front-runner Hillary Rodham Clinton as weak on the world stage. "Everywhere in the world that Hillary Clinton has touched is worse off today than before she and the president took office," Walker said.

He repeated his criticisms of Iran and the proposed nuclear deal that Congress will consider in September. But the greatest U.S. threat, Walker says, is the Islamic State militant group that has taken hold of portions of Iraq and Syria and is spreading elsewhere in the region. Walker called the fighters "agents of pure evil."

He called for toppling Syrian President Bashar Assad by recruiting and supporting "fighters in Syria who oppose both ISIS and Assad." The U.S. is in the process of training Syrian rebels to take on the Islamic State, though few have actually become battle-ready.

Besides fighting enemies overseas, Walker proposed securing the U.S.-Mexico border; bolstering counterterrorism and surveillance programs; and using economic sanctions to cut off financial capabilities in Syria and Iran.

As a governor, Walker does not have any active role in American foreign policy or have a security clearance to get briefings from military leaders or U.S. intelligence operations. Walker has no military service record. He has conducted foreign trade missions as governor, including a 2013 trip to China where he met with Xi.

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AP National Security Writer Robert Burns in Washington and Scott Bauer in Denison, Iowa, contributed to this report.

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