Philadelphia ? Sen. John Kerry cited the Iraq war and a huge cache of missing explosives Monday as proof President Bush has “failed the test of being commander in chief.”

The Republican slammed his rival as “consistently and dangerously wrong” on national security matters. But he fell silent on the disappearance of 377 tons of high explosives in Iraq, leaving it to aides to explain.

Public polls in the major battleground states of Pennsylvania, Ohio and Florida were so close that both camps had cause for optimism — and room for doubt. And with only eight days to go, there were signs that the field of competition might be widening.

Democrats fretted about a tight race in Hawaii and made plans to advertise to voters in the state.

Polls showed a tightening race in Arkansas, a state the president won four years ago and the Democrats had virtually given up for lost this time. The president’s high command was concerned, as well, about New Hampshire, in Bush’s column four years ago, trending Kerry’s way in the race’s final days.

Long-planned events blended with the unexpected in a campaign already marked by unpredictability.

Former President Clinton joined Kerry at a noontime rally in Philadelphia that drew tens of thousands. “If this isn’t good for my heart, I don’t know what is,” Clinton said, looking thinner seven weeks after bypass surgery.

Clinton also plans to campaign without Kerry this weekend in Nevada, New Mexico and Arkansas.

Supreme Court officials announced that Chief Justice William H. Rehnquist, 80, was undergoing treatment for thyroid cancer. The statement served as a reminder that the next president is likely to have more than one appointment to an aging court that is divided on abortion, gay rights and more.

Word of the disappearance of explosives from a military installation in Iraq was like a campaign gift to Kerry, and he quickly put it to use.

Former President Bill Clinton waves to supporters, with presidential candidate John Kerry at his side, as they take the stage at a massive campaign rally in Philadelphia. Clinton on Monday made his first public appearance following heart surgery.

Failure to secure the material was “one of the great blunders of Iraq, one of the great blunders of this administration,” the four-term Massachusetts senator said in New Hampshire, his first campaign stop of the day.

Bush gave as good as he got. “On Iraq, my opponent has a strategy of pessimism and retreat,” he said in Greeley, Colo.

That was mere warmup, though. He accused Kerry of “throwing out the wild claim that he knows where Osama bin Laden was in the fall of 2001 — and that our military had a chance to get him in Tora Bora.”

That was a reference to Kerry’s frequent assertion that the administration “outsourced” the job of hunting down bin Laden to Afghan warlords.

Beyond Iraq, Bush cited Kerry’s opposition to the first Persian Gulf War, his proposal for cuts in the intelligence budget in 1994 and his position on former President Reagan’s defense buildup in the 1980s. Together, they show that “on the largest national security issues of our time, he has been consistently and dangerously wrong.”