"My family loves Belle, but she can make a mess and we have to clean it up," Sestak says in the ad. "I think about Belle when I see Congressman Toomey's ads attacking me."
The most memorable image of the television spot: a shot of Sestak throwing away what appears to be a bag of Belle's you-know-what.
The Toomey campaign dismissed the ad as an attempt by Sestak to defend himself for supporting "every single bailout" of the last two years: "Too bad his defense is full of 'poop.'"
The ad may have been an unusual play for Sestak, but with nearly every poll taken since his primary victory over Sen. Arlen Specter this spring showing him trailing Toomey, the former Navy vice admiral and two-term Congressman is trying to get voters' attention. And it may be working.
Sestak and Toomey will meet for their first televised debate of the general election on Wednesday night in Philadelphia at 7 p.m. ET. The debate, which will be held at the National Constitution Center, will be moderated by ABC's George Stephanopoulos and Jim Gardner of local ABC affiliate WPVI.
Democrats have been touting a new internal poll released last week, as well as one public survey out on Tuesday, showing Sestak a few points ahead of Toomey. Though other recent polls indicate Toomey remains the frontrunner, Republican political operatives privately acknowledge that the race is getting closer.
ABC News has moved the race from "Lean Republican" to "Toss Up."
Earlier this week conservative commentator Erick Erickson posted an item on his blog, Red State, headlined "Who Can Help Pat Toomey?" He included a plea for supporters to travel to Pennsylvania to volunteer for Toomey or donate to his campaign.
"Quite frankly, we haven't done enough around here for Pat Toomey," Erickson wrote." Anything we can do to help him we should."
Also helping are the national party committees, which have been investing heavily in the race. Conservative outside groups have pumped millions into the race on behalf of Toomey, and the National Republican Senatorial Committee has pledged to spend millions more before Election Day. Toomey's old organization, the Club for Growth, has invested more than $1 million to oppose Sestak, according to campaign finance data compiled by the Sunlight Foundation, a watchdog group.
But Democrats have been active too. The Democratic Senatorial Campaign Committee has spent just short of $5 million on the race, with a series of ads attacking Toomey for his ties to Wall Street and his stance on trade with China. One of the ads suggests, "Maybe he ought to run for Senate in China."
Both candidates have also been strong fundraisers. Sestak raised $3.3 million during the third quarter compared to $3.8 million for Toomey. Sestak had slightly more cash on hand than his opponent -- $2.7 million in the bank to $2.3 million -- an obstacle that Toomey's team brushed off.
"We've outraised Congressman Sestak every single quarter," Toomey spokeswoman Nachama Soloveichik said in a statement, "There are so many things that we have going for us in this race."