WASHINGTON — For Democrats trying to reclaim the White House, the numbers have been tantalizing.

In winning Tuesday's primary in the key swing state of Wisconsin, Sen. Barack Obama drew support from tens of thousands of Republicans and independents. He pulled off the same feat in his landslide victory in the Virginia primary the week before, suggesting he could win the state in November. In South Carolina, he had more votes than the top two Republican contenders put together. In Kansas, his total topped the overall GOP turnout.

Obama has argued that he can redraw the political map for Democrats by turning out unprecedented numbers of young voters and blacks, and by attracting independents and even Republicans. But the picture emerging of his appeal in GOP strongholds and in swing states, even as he widens his delegate lead over Sen. Hillary Rodham Clinton of New York, is more complex than his claim to broad popularity in "red state" America might lead one to believe.

Obama, of Illinois, posted big wins over Clinton in caucuses in Plains and mountain states such as Kansas, Nebraska and Idaho, but Republicans in those states scoff at the suggestion that victories in the small universe of Democrats there translate into strength in November. In Tennessee and Oklahoma, Obama lost by wide margins to Clinton, who lived in nearby Arkansas. He narrowly won the primary in the swing state of Missouri, but did so thanks to the state's solidly Democratic cities, losing its more rural, and more conservative, areas to Clinton.

"If he's the nominee ... he'll start off with a good urban base, but he'll have to get out and develop these other areas," said former Tennessee governor Ned McWherter, a Democrat and Clinton supporter.

Clinton, making her own electability case, says she is more tested against Republican attacks and more able to turn out large numbers of women and Latinos.

CASE FOR CROSSOVER

In response, Obama says he would be likely to pick up most of her supporters in the fall, while many of those now favoring him — independents, men, young voters and blacks — may back Sen. John McCain, R-Ariz., or stay home if she is the nominee.

But he also has offered a more ambitious case for himself. Clinton envisions holding on to the base of blue states and picking up one or two swing states, such as Ohio, Florida or Nevada. Obama has conjured visions of a Reagan-style nationwide sweep, which, he says, would give him the influence — and the big majority in Congress — to attain the bold goals that skeptics call unrealistic for a young man with little Washington experience.

"We aren't going to have 47 percent on one side, 47 percent on the other side, 5 percent in the middle, and they all live in Ohio and Florida and you only campaign in two states," Obama often tells audiences.

His talk of exploding the map has been helped by McCain's emergence as the likely GOP nominee, since McCain has received relatively weak support in many of the red states in which Obama hopes to do well, in the South and Plains. But the primaries indicate he has a long way to go in making significant inroads in Republican states.

The red states where he has won have tended to be in the Deep South, where victories were based on overwhelming support from blacks, or in mostly white states in the Midwest and West, where a core of ardent backers carried him in caucuses, which favor candidates with enthusiastic supporters. He has not fared as well in areas that fall in between in demographics.

BIG DEMOGRAPHIC GAPS

Some analysts say this suggests that Obama will have an easier time with white voters in more racially homogeneous GOP-leaning states than in states with a more difficult racial dynamic. The University of Kansas' Burdett Loomis points to Interstate 70, which cuts across Kansas, Missouri and southern Illinois, as a sort of dividing line between the red-state areas to the north, where Obama has done well, and areas where he has struggled.

"You get below I-70, and race may play a role," he said. "You get to southern Missouri, and you're really moving south. And Oklahoma has some of those elements, too."

McWherter, the former Tennessee governor, said the results in his state showed the limits of Obama's appeal. Obama won the big cities, where Democrats are mostly African-American. He also won an affluent Nashville suburb that has voted heavily Republican in recent years, suggesting that Obama might pick up crossover support from wealthy Southerners in the fall.

But, McWherter noted, Obama lost the rest of the state.

The Obama campaign says that could be overcome with time in a general-election campaign. "He does fairly well with rural voters in certain places, but there's no question that Barack's going to have to get better acquainted with these voters," adviser Steve Hildebrand said.

The campaign points to Virginia, where exit polls show that he won a slight majority of white voters in varied economic areas across that red state.

Less clear is how Obama would fare in other red states.

John Bruce, a political scientist at the University of Mississippi, said it would be tough to win his state, which has a higher share of black residents than any other state, 37 percent. Obama would need deeply depressed Republican turnout, the votes of almost everyone who backed Clinton in the primary and a big chunk of independents. "He can do it, but it's that shot from half-court," Bruce said.

In Kansas, the Democratic caucus turnout of 37,000, while much higher than normal, was a fraction of the more than 1 million Kansans who vote in presidential elections.

But Annabeth Surbaugh, the Republican chairwoman of a Kansas City suburb, noted, "He may take (Kansas), not because he'd take it from Republicans but because he's getting people who haven't been in it before. I see it as a phenomenon. I wouldn't put money on him, but I wouldn't bet against it, either."