Hurricane Gustav has blown the presidential race into uncharted waters.

Never in living memory has a national political convention been overwhelmed by such a potentially huge natural disaster.

"One of the things we know about a hurricane is that many times they do the unpredictable," Sen. John McCain said Sunday afternoon as organizers of the convention that will nominate him for president upended their intricately scripted plans.

Gustav's political impact promises to be just as hard to forecast as its path toward the Gulf Coast, confronting Republicans with anything from a catastrophe to an unexpected opportunity to demonstrate leadership instead of talking about it.

By radically truncating their convention, at least for now, the Republicans are staging a near-oxymoron -- a political convention that could end up being free of politics and devoid of speeches. While that robs them of their nationally amplified megaphone, it also allows them to stand above the fray, raising money for hurricane victims and praying for them aloud.

McCain instructed his GOP brethren in a satellite feed from St. Louis on Sunday that the time has come to "take off our Republican hats and put on our American hats."

Brian Sullivan, a prominent Republican activist in Minnesota, said McCain's decision to scale back the convention was showing that the likely Republican nominee was willing to take a "do what's right, and things will shake out" approach, just as he did, Sullivan says, in supporting the troop surge in Iraq.

"We may not have the convention we thought we would have, but we can still show that the Republican Party is one that can respond to a crisis," said Charlie Weaver, head of the Minnesota Business Partnership and a Republican activist.

Neither the Republican nor the Democratic playbooks have a page designed to deal with the hurricane's political fallout. And while the stakes are highest for the GOP, the Democrats face risks, as well.

"Democrats would be just well advised not to engage in any public analysis of how the hurricane affects the Republican Convention, one way or another," said David Lillehaug, former U.S. attorney for Minnesota and a Democratic insider in the state. "I don't think there's any upside whatsoever in having Democrats talking about the politics of hurricanes."

Haunted by Katrina

For the Republicans, most immediately, the decision by President Bush and Vice President Dick Cheney to cancel their appearances at the convention tonight resolves a painful quandary for the party.

While much of the party's base remains devoted to Bush, his record-setting unpopularity with the general public meant that convention planners had to balance honoring the incumbent with efforts to distance McCain from him.

Sen. Norm Coleman addressed the dilemma, through an ironic image, last week, when he told members of the Republican National Committee that a McCain administration would be a vast improvement over the federal bureaucracy that responded ineffectively to Hurricane Katrina three years ago.

"We will not see the mistakes of Katrina repeated," McCain declared Sunday.

Memories of that slow and confused response, widely seen as the nadir of Bush's presidential performance, are arguably the biggest threat Gustav poses for the GOP.

If the relief effort is once again bungled, it will eloquently reinforce for voters the Democrats' campaign theme that change is needed in Washington and that McCain cannot provide it.

If, however, the response comes off well this time, it could defuse Democratic accusations of Republican incompetence and indifference and suggest that lessons have been learned.

The unprecedented dilemma facing the Republicans was being watched intently.

The Republicans were "more at risk than they have upside," said Jon Austin, a former spokesman for Northwest Airlines who owns his own corporate consulting company in Minnesota. "They're going to have to play improv."

Austin, whose company helps clients with crisis management, said the problem for the Republicans is that even if the hurricane response goes well many voters will simply conclude "the system worked -- this time."

At the same time, he said, a good response may lead others to conclude they are not simply "watching the party of the rich, the party of the "I-don't-care.'"

Hard to talk about

The sensitivities of the situation were evident as Republicans tried Sunday to minimize any political considerations. "It's a little hard to talk about," Vin Weber, a longtime consultant in Washington and former Minnesota congressman, said of the politics of the hurricane. Weber said that he was serving as an informal adviser, and that he was receiving many phone messages and e-mail messages as Republicans tried to figure out what to do.

But he added: "I just don't want to go any further. I don't want to make this more political."

Minneapolis Mayor R.T. Rybak, who heads the Obama campaign in Minnesota, took a similar line. "I think the most important thing the next couple of days is to focus on the Gulf Coast and after that, let the chips fall where they may," he said. "No politics."

Dan Hofrenning, a political science professor at St. Olaf College, said the Republicans must avoid a scenario where millions of Americans are watching "a split [TV] screen between a Category 5 hurricane and a nominating party" moving ahead without interruption. That, he said, "is a disaster."

But the Democrats, too, faced some risks and were determined not to appear callous or opportunistic.

On Sunday, party staffers were cranking up the operation of their anti-convention war room at a labor hall a couple of blocks from the Xcel Energy Center. They had planned to unveil their "More of the Same Media Center" during an afternoon reception for journalists, but abruptly canceled the event early in the afternoon.

"Obviously, we're monitoring the situation with Gustav just like [the Republicans] are," said Damien LaVera, a spokesman for the Democratic National Committee. "This isn't a political moment -- it's a moment for the entire country."

The party also canceled a news conference scheduled for this morning. "But things are pretty much in flux because of what's happening in the Gulf," LaVera said.

Rybak said Obama campaign officials had sent instructions from their Chicago headquarters to cancel all parties, rallies and other campaign events for the time being.

Staff writer Patricia Lopez contributed to this report. • 612-518-3182 • 651-677-5011