Barack Obama's camp accused Hillary Clinton on Monday of trying to scare voters on the eve of the Pennsylvania primary, as she rocked their White House race with a dark campaign ad featuring images of Osama bin Laden.
The Democratic foes squabbled over who was qualified for what Clinton calls "the toughest job in the world" during a frenzied sprint to Tuesday's nominating showdown, which polls suggested she would win.
As the campaigns cranked up huge turnout operations, attention was turning to the scale of any Clinton victory. Most observers think she needs a wide margin to breathe life into her uphill bid for the Democratic nomination.
Clinton's ad featured Pearl Harbor, Al-Qaeda mastermind bin Laden and Hurricane Katrina, mirroring a "3:00 am phone call" spot credited with helping her to win in Texas and Ohio last month.
She played off the script of her ad during a lunchtime rally in downtown Pittsburgh.
"If you can't stand the heat, get out of the kitchen," Clinton said, using former US president Harry Truman's famous catchphrase. "I am very comfortable in that kitchen making those decisions."
As the narrator of the Clinton ad speaks, images flash by of the fall of the Berlin Wall, bin Laden and the devastating hurricane that swamped New Orleans in 2005.
"You need to be ready for anything -- especially now, with two wars, oil prices skyrocketing and an economy in crisis," the male narrator intones. "Who do you think has what it takes?"
The 30-second broadcast does not mention Obama by name, but the Illinois senator's spokesman Bill Burton fired off a robust response and brought up Clinton's vote in 2002 to authorize the Iraq war, which his boss opposed.
"It's ironic that she would borrow the president's tactics in her own campaign and invoke bin Laden to score political points," Burton said.
"We already have a president who plays the politics of fear, and we don't need another," he said.
In an interview on CNN's Larry King Live Monday, Clinton pressed home her claim that despite trailing Obama in nominating wins and elected delegates, she was still the most likely Democrat to beat Republican John McCain in November.
"I think he (Obama) can win, but I think I will win," she said, and also accused her rival's campaign of going "increasingly negative" in the run up to the Pennsylvania primary.
Late polls appeared to show that Clinton was again set for victory in a state packed with her working-class supporters, although by far less than the 20-point margin she once enjoyed in the polls.
She led Obama 52 percent to 42 percent in a Suffolk University survey. A Quinnipiac University poll had her up 51-44 percent, one point up from last week in the same survey.
"A win is a win," the New York senator said on Larry King, and reiterated that she had no intention of giving up after Tuesday but planned to keep fighting until the primary process ends in June.
In an interview with Pittsburgh radio station KDKA, Obama said he was "not predicting a win" in Pennsylvania but added: "I am predicting it is going to be close and we are going to do a lot better than people expect."
Clinton's huge task in overcoming her rival was revealed by the latest figures showing Obama's staggering advantage in fundraising.
The Federal Election Commission filings showed the Illinois senator had 42 million dollars in cash in hand for the primary season at the start of April. Clinton had only nine million dollars in hand.
The Clinton campaign said Obama was outspending her three to one in Pennsylvania.
"If Senator Obama can't win a big swing state like Pennsylvania with that enormous spending advantage, just what will it take for him to win a large swing state?" Clinton spokesman Howard Wolfson said.
Neither Democrat is expected to reach the tally of 2,025 nominating delegates to claim the nomination outright.
So Clinton needs to convince nearly 800 superdelegates -- top party officials who can vote how they like at the party's August convention -- that it would be too risky to pick the inexperienced Obama.
Oscar-winning documentary film-maker Michael Moore Monday endorsed Obama, decrying Clinton's "downright disgusting" campaign tactics which he said were designed to "smear the black man."