Clinton leads in Pennsylvania polls and needs to win the state handily to make an argument to superdelegates, who could decide the nomination in her favor even if she trails in pledged delegates, that she deserves the nomination.
The Pennsylvania vote, Clinton's chief strategist Mark Penn told reporters, will be a "very significant test of who could really win the general election."
"We believe this will show Hillary is ready to win, and that Senator Obama really can't win the general election," Penn said.
Pennsylvania Governor Ed Rendell called what he characterized as the Obama campaign's attempts to "diminish" the significance of the Pennsylvania vote "off-putting."
He said Pennsylvania's primary will be a "true test of someone's national appeal" because of the state's diversity, citing the presence of farming, big cities, coal mining, and both a midwestern and east coast "tinge."
"This is not a solid blue state," Rendell said. "This is a purple state. And we need a candidate who can win here."
Philadelphia Mayor Michael Nutter took aim at a recent memo from the Obama campaign critiquing and editing a Clinton memo sent yesterday.
The memo is "one of the silliest things I've seen in recent times," Nutter said. "If somebody on my staff wrote something like that, I'd fire them, because it just doesn't make any sense."
Pennsylvania is "a critical state and everybody knows it for the general election," he added.
Both Penn and Rendell pushed the notion that Pennsylvania is one of four states – the others are Ohio, Florida and Michigan – that Democrats need to do well in if they want to win in November. (Clinton won in all three of the other states, though Obama wasn't on the ballot in Michigan and the candidates did not compete in Michigan or Florida because the states violated DNC rules by holding their primaries early.)
The four states are "dominated by swing voters who are critical to a victory in November," Penn said.
Added Rendell: "We need to win three of four."