(CNN) -- Hillary Clinton and Barack Obama haven't crossed paths yet during their weekend barnstorming across Pennsylvania, but they have invoked each other's names at virtually every whistle-stop during the final blitz before Tuesday's primary.
Sens. Hillary Clinton and Barack Obama are attacking each other over health care plans and negative ads.
Each candidate says the other is unfit to lead the country.
Clinton has attacked Obama for his recent comments about some small-town Americans, his heath care plan and his relative Washington inexperience. Obama has countered by taking aim at Clinton over her acceptance of money from political action committees, her health care plan and her Washington experience.
But the most oft-repeated charge -- the one mentioned at virtually every stop -- is negative campaigning.
"I just heard that my opponent has put out an ad attacking my health care plan, which is kind of curious because my plan covers everybody, and his leaves out 15 million people, just leaves them out in the cold," Clinton said at a campaign rally in York, Pennsylvania, on Saturday. "Instead of attacking the problem, he chooses to attack my solution." Watch a panel predict how Tuesday will play out »
For his part, Obama accused Clinton of looking to create "fake controversy" around him in the race's final days.
"In the last few months, she's launched what her campaign calls a 'kitchen sink' strategy of negative attacks, which she defends by telling us that this is what the Republicans would do. She says that's how the game is played," he told a Philadelphia crowd.
In Paoli, Pennsylvania, he accused her of "slash-and-burn politics."
The New York senator, Obama said at an appearance in Wynnewood, Pennsylvania, was "throwing everything at me and seeing if something sticks."
In response, Clinton spokesman Phil Singer e-mailed reporters a link to a quiz on the campaign's Web site that asked them to decide who had uttered quotes attacking Clinton: a member of Obama's campaign or a Republican.
The charges and countercharges aren't limited to the candidates' stump speeches. Over the past three days, both launched negative robo-calls, tough mailers and attack ads alleging special interests influence their opponent. And on dueling conference calls, surrogates used some of the race's harshest language to date.
On an Obama conference call with reporters Saturday, Gen. Walter Stewart said Clinton's misstatements about her trip to Bosnia as first lady mean she "lacks the moral authority" to lay a wreath at the Tomb of the Unknowns at Arlington National Cemetery in Virginia.
At a campaign event at Pennsylvania's California University shortly after the call, Clinton said that the Illinois senator "always says in his speeches that he is running a positive campaign but then his campaign does the opposite."
Later, Clinton communications director Howard Wolfson sent reporters a memo charging that Obama "flooded airwaves, radio, phone lines and mailboxes with negative and false attacks against Hillary" in the previous 48 hours, calling Stewart's remarks "the most outrageous attack of the campaign."
The tough words underlie the high stakes and the closeness of the race.
After leading by 20 percentage points just a few weeks ago, Clinton's lead has shrunk to the single digits in the most recent CNN Pennsylvania Poll of Polls, an average of recent campaign surveys.
Clinton has a strong base in the state with solid support from working-class white voters, Catholics and seniors -- three powerful and potentially decisive voting blocs.
But a record number of new voters and party-switchers in Pennsylvania -- the most in any primary contest, and second in number only to the 2004 general election -- propelled Obama into contention in the state.
On Friday, he drew the largest crowd of his campaign, an estimated 35,000 people, to an outdoor rally in Philadelphia.
The risk for both is that supporters may be turned off by the race's negative tone -- a danger both recognize.
"You've been watching this campaign for a couple weeks, at least here in Pennsylvania, and let's face it, it's not pretty," Obama acknowledged Saturday in Paoli. "But the issue is not whether people are saying nasty things. The problem is that it's a distraction from solving the problems that have to be solved." E-mail to a friend
CNN's Peter Hamby and Chris Welch contributed to this report.