He didn't. He has maintained a consistent lead of about two to three points (closer to three points) nationally since the end of the debates. What you are seeing in this poll is the inevitable statistical noise of a tracking poll.
Wait a minute. Look at the numbers here from the last three days.
Net Leaned Vote, Likely Voters:
Other Neither Would No
Bush Kerry Nader (vol.) (vol.) not vote op.
10/25/04 48 50 1 * * 0 1
10/24/04 48 49 1 * 1 0 1
10/23/04 49 48 1 * 1 * 2
The numbers are
Bush 49 48 48
Kerry 48 49 50
If my math is good that is Bush 49 + 48 + 48 = 145 devided by 3 = 48.3
Kerry 48 + 49 + 50 = 147 devided by 3 = 49
So it should be Bush 48.3 Kerry 49
So is my math wrong or did they round a whole number up for Kerry?