Sen. Hillary Clinton's lead over Obama has been cut to four points, 50% to 46%. Just a couple weeks ago Clinton held a lead over 20 points in some polls.
Key factor: "Obama is benefiting from the decided nature of the Republican contest. That's increasing the number of Republicans and independents who plan to cast their ballots in the Democratic primary next week, and Obama leads those groups 80% to 13% and 64% to 33% respectively. Clinton actually has a 56% to 40% edge among self identified Democrats."