After maintaining hurricane strength through the morning, Isaac weakened to a tropical storm Wednesday afternoon with 70 mph winds and was expected to continue losing strength. It came ashore at 7:45 p.m. EDT Tuesday with 80 mph winds near the mouth of the Mississippi River, driving a wall of water nearly 11 feet high inland and soaking a neck of land that stretches into the Gulf.

The storm stalled for several hours before resuming a slow trek inland, and forecasters said that was in keeping with the its erratic history. The slow motion over land means Isaac could be a major soaker, dumping up to 20 inches of rain in some areas. But every system is different.

In Mississippi, the main highway that runs along the Gulf, U.S. 90, was closed in sections by storm surge flooding. At one spot in Biloxi, a foot of water covered the highway for a couple of blocks, and it looked like more was coming in. High tide was likely to bring more water.

In Pass Christian, a Mississippi coastal community wiped out by hurricanes Camille and Katrina, Mayor Chipper McDermott was optimistic Isaac would not deal a heavy blow.

"It's not too bad, but the whole coast is going to be a mess," he said.

Tens of thousands of people had been told ahead of Isaac to leave low-lying areas of Mississippi and Louisiana, including 700 patients of Louisiana nursing homes. Mississippi shut down the state's 12 shorefront casinos.

The hurricane also canceled commemoration ceremonies Wednesday for Katrina's 1,800 dead in Louisiana and Mississippi.

The storm drew attention because of its timing ---- coinciding with the Katrina anniversary and the first major speeches of the Republican National Convention in Tampa, Fla. Republican presidential candidate Mitt Romney was considering whether to visit the Gulf Coast after Isaac.

Isaac also posed political challenges with echoes of those that followed Katrina, a reminder of how the storm became a symbol of government ineptitude.

President Barack Obama sought to demonstrate his ability to guide the nation through a natural disaster, and Republicans tried to reassure residents as they formally nominated former Massachusetts Gov. Mitt Romney as their presidential candidate.

There was already simmering political fallout from the storm. Republican Gov. Jindal, who canceled his trip to the convention in Tampa, said the Obama administration's disaster declaration fell short of the federal help he had requested. Jindal said he wanted a promise from the federal government to be reimbursed for storm preparation costs.

FEMA Administrator Craig Fugate said such requests would be addressed after the storm.

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