(CNN) - Barack Obama continues to chip away at Hillary Clinton's lead in the crucial state of Pennsylvania, a new Quinnipiac poll out Tuesday shows.
The New York senator's lead over Obama now stands at 6 points in the new poll, 50-44 percent. That compares to the 9 point lead Clinton held in a similar survey released 5 days ago, and an 11 point lead in a Quinnipiac survey late last month.
Specifically, Clinton has lost ground among white voters and men: She now holds an 18 point lead among whites, down from a 25 point gap in last week’s poll, and trails Obama by 4 points among males. Last week, the two drew equal support from men.
But Clinton continues to remain strong with her core voting bloc of older voters and white women, and likely Pennsylvania Democratic voters rate her more favorably than Obama - 71 percent for Clinton and 67 percent for Obama.
With the latest Quinnipiac poll, CNN's poll of several recent surveys show Clinton's lead over Obama in Pennsylvania now averages 6 percentage points. That gap is 1 point less than Monday’s poll of polls and 5 points less than a CNN poll of polls on Friday.
What's behind the shift?
"Obama has outspent Hillary Clinton three to one just on television advertising in Pennsylvania. He spent more than $3 million trying to get his name out and his message out to Hillary Clinton's $1 million," said Mark Preston, a CNN political editor.
The Illinois senator has also heavily benefited from the Service Employees International Union, which according to recently filed FEC reports has spent well over $700,000 on get-out-the-vote-efforts there.