John Kerry (search), telling fellow combat veterans he's their "true brother in arms," said Wednesday that President Bush's plan to withdraw U.S. troops from Europe and Asia would weaken U.S. security and embolden nuclear-armed North Korea.

"This is clearly the wrong signal to send at the wrong time," the Democratic presidential candidate said at the Veterans of Foreign Wars' (search) 105th annual convention, borrowing a line Bush has used against him.

Some Bush supporters and a few fellow veterans have been raising questions about Kerry's military record, which has been a cornerstone of his presidential campaign. Senior Democrats inside and outside the campaign say they're worried about indications, some based on polling, that the criticism might be undercutting gains Kerry made against Bush in the Democratic National Convention, with its spotlight on his combat record and military honors from the Vietnam War (search).

Some Democrats are urging Kerry to fight back against the criticism, which gained steam this month with a TV ad featuring fellow veterans questioning his record. Kerry campaign officials, speaking on condition of anonymity, said he may have to do so.

Addressing the same VFW crowd two days earlier, the president announced a seven- to 10-year plan to withdraw up to 70,000 U.S. troops from Cold War bases in Europe and Asia. He accused Kerry of sending "the wrong signal" by promising to try to withdraw U.S. troops from Iraq (search) within six months of taking office.

Along with the economy, national security has emerged as a major theme in a campaign shadowed by war and terrorism.

The challenger hopes to convince voters he is tough enough to lead the nation against terror. The incumbent, his approval ratings hurt by the war in Iraq, is casting himself as a tested commander in chief who can guide the nation back to peace and prosperity.

Both men call the other lacking on defense, with Kerry now taking aim at Bush's troop-shifting plans.

"Let's be clear: The president's vaguely stated plan does not strengthen our hand in the war against terror, and in no way relieves the strain on our overextended military personnel," Kerry told the crowd after repeatedly reminding the veterans of his own combat experience in the Vietnam War.

"Why are we unilaterally withdrawing 12,000 troops from the Korean Peninsula at the very time we are negotiating with North Korea -- a country that really has nuclear weapons?" the Massachusetts senator said. That last phrase was a reference to Iraq, which apparently did not have nuclear weapons when Bush ordered the invasion, with support from Kerry and others in Congress.

Bush, campaigning in Wisconsin, said Wednesday, "Our troop deployments were configured for the Cold War -- we were configured to fight an enemy that no longer exists. ... When you can replace land troops with more effective aircraft it means people are stationed at home and they can be deployed rapidly and it's less unsettling times for our troops, less rotations, less pressure on the system, plus taxpayer savings."

White House spokesman Scott McClellan noted that Kerry expressed support on Aug. 1 for possible redeployment of U.S. troops throughout the world, including in Korea.

Kerry foreign policy adviser Rand Beers said Kerry would consider moving some U.S. troops farther south on the Korean Peninsula to avoid a strike from the North. But he would not move them off the peninsula, Beers said, unless such action was part of a broader agreement with North Korea to scrap its nuclear program and reduce its conventional forces.

On Monday, Bush received a commander-in-chief's welcome from the VFW in this Republican-leaning city, drawing loud cheers of support. The veterans, who tend to vote more Republican than Democratic, gave Kerry a polite welcome.

Large portions of the crowd applauded each of his many promises to protect veterans' benefits. Smaller portions vocally backed his points on Iraq and terrorism. Some veterans sat with arms folded, while others stood and clapped.

One man heckled Kerry, calling him a liar.

"I'll say it myself. He's a liar," said John Ranson of Fort Thomas, Ky., a 57-year-old Vietnam veteran who sat a few feet away from the heckler. He said Kerry had not supported U.S. troops as a senator or three decades ago as a returning Vietnam veteran who protested the war.

But there was no shortage of Kerry supporters, including some who voted for Bush in 2000. Dale Hall, 49, of Franklin Park, Ill., said Bush has "got a mess overseas. I stand behind the troops, of course, but he's not done a good job."

Kerry tried to connect with the crowd, saying that if elected "you will have a true brother in arms" who will protect veterans' benefits and improve the nation's security.

He did not mention that Bush served stateside in the Texas Air National Guard, though Kerry's allies have accused the president of using family connections to stay out of Vietnam.

Bush's troop announcement on Monday was filled with political implications. His advisers predicted the plan would please swing voters weary of Iraq, though it involves troops in Europe and Asia, not the Mideast. Bush was in Wisconsin on Wednesday, promising extra education benefits for National Guard members and reservists.

Kerry suggested that Bush's troop plan would upset allies, whose help is needed as the U.S. fights the Al Qaeda terror network in 60 countries.