"We've got to have a Democratic Senate to do it," he said, adding that in many states the DSCC faces a tough fight in 2014.
Obama said that Washington may seem polarized, but that the country at large is not necessarily so divided and that politicians have to "sync up that spirit of goodness."
The fund-raiser was held in a large white tent set up in the backyard of Cohen's stone house in West Mount Airy. Residents lined up along sidewalks to cheer the president's motorcade as it wound through the neighborhood.
The guests were just finishing up dinner when the president suddenly entered.
Cohen, executive vice president at Comcast and a longtime Democratic Party powerhouse, said the event raised $1 million for the DSCC. Obama nodded and mouthed, "Good job."
Diners at the $10,000- to $32,400-a-plate dinner included Sens. Robert Casey of Pennsylvania and Michael Bennet of Colorado, plus Mayor Nutter.
Introducing the president, Cohen referenced the Hebrew term dayenu, an expression of gratitude that means "it would have been enough."
He listed several accomplishments of the Obama administration, including repealing "Don't Ask, Don't Tell" and ending the war in Iraq, and after each, the crowd repeated: "Dayenu."
Obama offered his version for Cohen:
"If David and Rhonda [Cohen's wife] had just hosted one of my first fund-raisers after I'd been elected to the United States Senate, that would have been enough. Dayenu."
He elaborated, prompting laughter: "I have been here so much - the only thing I haven't done at this house is have seder dinner."