DAYTONA BEACH, Fla. — Barack Obama made the calamity on Wall Street the central theme of his case against John McCain on Saturday, invoking the crisis to pound his rival on Social Security, health care and government reform.

The scope of Obama’s argument demonstrated how the biggest financial bailout since the Great Depression has shifted the terms of debate in the White House contest. In two days of campaigning across Florida, the Democratic presidential nominee made it the foundation of a wide-ranging assault on his Republican opponent. McCain, in turn, has used it to sharpen his criticism of Obama.

Playing off the pocketbook anxieties of the state’s huge elderly population, Obama reminded Floridians that McCain backed President Bush’s doomed effort to let Americans invest Social Security benefits in the stock and bond markets. If McCain had his way, Obama said, millions last week “would’ve watched as the market tumbled and their nest egg disappeared before their eyes.”

“I know Senator McCain is talking about a casino culture on Wall Street, but the fact is he’s the one who wants to gamble with your life savings,” Obama told 2,500 supporters in a theater at Bethune-Cookman University.

In fact, McCain has favored giving only future retirees — not current beneficiaries — the option to invest Social Security savings.

McCain spokesman Tucker Bounds called Obama’s attack “a desperate attempt to gain political advantage using scare tactics and deceit.”

“John McCain is 100 percent committed to preserving Social Security benefits for seniors, and Barack Obama knows it,” he said.

As Obama wrapped up his Florida trip with rallies in Daytona Beach and Jacksonville, McCain took a break from campaigning Saturday. He attended a football game and his 50th class reunion at the Naval Academy in Annapolis, Md.

Obama’s appeal for elderly support was part of a concentrated weeklong push by the Democrat in Florida. He plans to spend a few days in the Tampa Bay area this week in preparation for his first debate with McCain on Friday in Oxford, Miss.

Most polls have found Florida leaning toward McCain, but some recent surveys suggested the race was closer in the state that Bush won by 537 votes in 2000.

“We can win this thing without Florida, but boy, it’s a lot easier if we win Florida,” Obama told donors Friday night at a Miami fundraiser.

But Obama’s main focus Saturday was upheaval in the financial markets. Citing the breakdown in government oversight, he recalled McCain’s description of himself as “fundamentally a deregulator.” Obama read — verbatim, and with an exaggerated tone of sarcasm — a quote from an article on health care that McCain wrote in Contingencies, a trade publication for actuaries.

“Opening up the health insurance market to more vigorous nationwide competition, as we have done over the last decade in banking, would provide more choices of innovative products less burdened by the worst excesses of state-based regulation,” Obama read.

“So let me get this straight,” he said. “He wants to run health care like they’ve been running Wall Street. Well, Senator, I know some folks on Main Street who aren’t going to think that’s such a good idea.”