But the coalescing of party leaders around Obama continued Tuesday, as three more superdelegates -- New Orleans Mayor Ray Nagin, Rep. Joe Donnelly of Indiana and the District of Columbia Democratic party chair -- endorsed the Illinois senator.
"Senator Obama represents a new generation of leadership, one that can help heal the divisions of the past and unify this country so that together we can build a stronger future," Nagin said in a statement.
Interest is keen in the West Virginia primary, judging by a record turnout of more than 70,000 people who cast ballots in person before Tuesday in the state's liberal early voting system.
Clinton implored West Virginians in four stops Monday to send her forward with a convincing win.
"This may be the most important vote you've ever cast," she told a crowd in Fairmont. "Let's have a huge vote in West Virginia."
Obama made only one appearance in the state, talking up his love of country and conviction that veterans of the Afghanistan and Iraq wars deserve better care from their government when they come home.
"At a time when we're facing the largest homecoming since the Second World War, the true test of our patriotism is whether we will serve our returning heroes as well as they've served us," he said.
In every step now, he's mindful of the gathering struggle with McCain, a veteran both of politics and war who will exploit Obama's short national resume as surely as Clinton has tried to do.
Obama is mounting a two-week tour that will take him to the remaining primary states but concentrate on fall battlegrounds including Florida and Michigan.
Clinton won both states, although Obama had his name removed from Michigan's ballot, and no delegates were awarded. Restoring the delegates is a major part of Clinton's long-shot strategy for the nomination.
Clinton's last best hope is to use strong showings in West Virginia and Kentucky to make the case that Obama is weak among key Democratic constituents.
They are, most prominently, blue-collar, white voters, an abundant proportion of the electorate in West Virginia and a leading reason why Clinton ran strong in the state.
A strong Clinton victory would not materially change Obama's prospects nationally. But it would lay bare the racial divisions and other polarizing aspects of the protracted and often bitter Democratic contest.
Increasing numbers of Democratic primary voters have become entrenched behind their candidate and said they would not support the other candidate in the fall -- a rift the party is eager to start healing.
To that end, the party leaders known as superdelegates have been moving to Obama's side, 29 of them in the week since he routed Clinton in North Carolina and narrowly lost Indiana. Clinton added two superdelegates in the same period.
At that pace, he would reach the number of delegates needed to clinch the nomination -- 2,025 -- in three weeks, when delegates from the remaining primaries are included.
West Virginia had 28 delegates at stake Tuesday.