Senator Barack Obama (D) now leads former Mayor Rudy Giuliani (R) 43% to 41%, according to the latest Rasmussen Reports national telephone survey. Obama posts a 47% to 42% lead over former Senator Fred Thompson (R) (see crosstabs).

A month ago, Giuliani led Obama by two points. In both polls, the Democrat’s support remained steady at 43%. However, Obama had the edge on six of seven polls before that dating back to mid-July (see trend history). Those leads were typically modest, ranging from one to six points.

Fred Thompson trailed Obama by only one percentage point in October, but his current five-point deficit is consistent with the history of this match-up. Thompson has occasionally trailed by either double digits or just a point or two. But in eight out of 13 previous surveys his deficit ranged from three to seven points. And no matter how close to Obama he comes, Thompson has yet to actually tie him, let alone take the lead.

Since October, core support among all voters for Obama and especially Thompson has weakened. And Thompson's support from Republican primary voters has slid from as high as 28% in September, after he announced his candidacy on "The Tonight Show," to the low teens. Thompson started October with 25% support and began November with 15%. On November 14 he was down to 12% in the Rasmussen Reports daily Presidential Tracking Poll.

Individual polls can sometimes overstate volatility in a race, especially when the results carry a four percentage point margin of sampling error. One way of addressing this is to look at a rolling-average of three consecutive polls. Using this approach, Obama currently has a two-point advantage over Giuliani (44% to 42%). That margin has been steady at two or three points for several months.

Using the three-poll average, Obama now has a four-point advantage over Thompson, down from a six point edge in the previous set of three polls. This is the closest Obama and Thompson have been since July.

Upon entering the race, Thompson was seen by Republicans as the most conservative candidate in the field. He has lost that crown to former Massachusetts Governor Mitt Romney.

Romney, while struggling in national polls, continues to lead in the early voting states of Iowa and New Hampshire. Strength in early primary states is starting to be reflected in national sentiment. A commentary by Douglas Schoen argues if Romney’s showing in the first primaries matches the current polls, he could be well on his way to the nomination.

Thompson is now viewed favorably by just 39%, unfavorably by 46%—his second-highest unfavorable rating so far. Giuliani is viewed favorably by 47%, unfavorably by 49%. Obama is now at 45% favorable, 50% unfavorable.

Crosstabs and Historical Data available for Premium Members only.