Obama now leads in states with many older voters.
Obama sees potential in traditional red states such as Virginia, Colorado, and North Carolina. McCain looks to target blue states including Pennsylvania and Michigan.
A convincing win spurs the fight forward, but does little to close the gap in delegate count with Obama.
Her viability is at risk if she doesn't, analysts say.
She needs to win nearly all the remaining contests, analysts say, and persuade superdelegates that she has a better chance than Obama of beating John McCain.