A new Quinnipiac poll shows that Obama has cut into Hillary's lead in Pennsylvania, where she needs a decisive, if not overwhelming, win to keep her presidential hopes alive.

She leads Obama by six points, 50%-44%, down three points from only last week.

The shift is driven partly by Obama's showing among key swing constituencies -- whites, voters from the Philadelphia suburbs, and women -- 41% of whom now back Obama, up from 37% last week. Other Q-poll numbers:

*White voters for Clinton 56 -- 38 percent, down from 59 -- 34 percent last week.

*Black voters back Obama 75 -- 17 percent, compared to 73 -- 11 percent.

*Men are for Obama 48 -- 44 percent, compared to a 46 -- 46 percent tie last week.

*Voters under 45 go with Obama 55 -- 40, while older voters back Clinton 55 -- 38 percent.

As I reported here recently, Obama told a group of California donors that if he were to come within 10 points of Hillary in the state, he'd call it a victory.

If he manages to keep it as close as today's survey, it will make it that much tougher for Hillary to make the case to super-delegates that she still has any kind of reasonable shot at closing the gap with Obama.