Vienna, Ohio ? Addressing a growing campaign controversy, President Bush suggested Wednesday that a missing cache of Iraqi explosives may have vanished before last year’s U.S. invasion — and accused his Democratic rival of “jumping to conclusions” without the facts in a way that undermined his credibility.

But Bush’s scenario about the fate of the 377 tons of high-explosive munitions was challenged by the comments of a high Iraqi science official, Mohammed al-Sharaa, who told the Agence France-Press news agency it would have been “impossible” for the explosives to be removed from the al-Qaqaa complex before Saddam Hussein’s fall.

Democratic nominee John F. Kerry, who on Monday pounced on the disclosure of the missing munitions as an example of what he called Bush’s “incredible incompetence,” fired back at Bush by accusing him of trying to duck responsibility for the incident.

The sharp new exchanges occurred as Bush went trolling for support from conservative Democrats in three large swing states. Accompanied by Georgia Sen. Zell Miller, a dissident Democrat, Bush called Kerry out of the mainstream of his party on issues ranging from national security to education to late-term abortion and same-sex marriage.

The closeness of the presidential race has magnified the importance of each emerging issue, and Monday’s disclosure by The New York Times that the munitions had disappeared despite requests from international weapons inspectors to secure them instantly became part of the campaign debate.

Kerry called it part of a pattern of Bush failures. The Bush camp answered by citing an NBC News report that the explosives were already gone when U.S. forces reached the site in April 2003; but the network later reported that the troops never searched for the munitions and paused there only briefly on the way to Baghdad.

Wednesday, in his first comments about the matter, Bush said the U.S. military was investigating “a number of possible scenarios, including that the explosives may have been moved before our troops even arrived at the site.”

Bush then tried to turn the issue against Kerry, accusing him of “denigrating the action of our troops and commanders in the field” and making “wild charges” even though a top Kerry adviser had acknowledged that the Kerry campaign did not have the facts.

“A political candidate who jumps to conclusions without knowing the facts is not a person you want as your commander-in-chief,” Bush told cheering crowds of supporters in Lititz, Pa., and later in Vienna, just outside Youngstown, and suburban Detroit.

Bush campaign officials said the president was referring to an interview with Fox News by Kerry’s chief national security adviser, Richard Holbrooke. He said weapons inspectors had warned the U.S. military that al-Qaqaa was a major weapons depot, then added, “I don’t know what happened. I do know one thing — in most administrations the buck stops in the Oval Office.”

The Kerry campaign accused Bush of distorting Holbrooke’s words, saying he was merely saying the particular facts needed to be pinned down.

And Kerry shot back at Bush at a stop in Rochester, Minn., saying the president had put U.S. troops in danger by failing to inspect al-Qaqaa to find out what had happened to the explosives.

“I say this to the president … for the sake of our brave men and women in uniform, for the sake of those troops who are in danger because of your wrong decisions, you owe America real answers about what happened, not just political attacks,” Kerry said.

“Our troops are doing a heroic job. The president, the commander in chief, is not doing his job,” Kerry continued. “You were put on notice, but you didn’t put these explosives on a priority list. … You didn’t guard the ammunitions dump, and now our troops are at greater risk.”