Although national primary polls do not reflect the actual state of the race like early state primary polls do (the outcomes of early contests influence later ones, candidates are not campaigning in the later states, voters in the later states are not paying close attention yet, etc.), they can be useful to look at occasionally. Candidates do pay attention to the national primary polls and sometimes develop their strategies based upon them. For instance, if they see a frontrunner developing in the national polls, they may begin to attack him. The media also like to look at national polls and may create narratives based on them.
For an example of the latter, note that the "Herman Cain is falling" narrative reflects the national polls much more than the polls in Iowa, South Carolina, and Florida, where Cain has still shown strength of late. Granted, there has not been sufficient polling in South Carolina and Florida over the past few weeks, so any new developments may be caught in the national polls first.
The following are the most recent polls taken nationally for the Republican primary:
National Primary Polls
11/20 Gingrich 24, Romney 20, Cain 17, Perry 11 (CNN)
11/20 Gingrich 26, Romney 22, Cain 14, Perry 06 (Quinnipiac)
11/17 Gingrich 22, Romney 21, Cain 16, Paul 09 (Gallup/USA Today)
11/15 Gingrich 23, Romney 22, Cain 15, Paul 08 (Fox News)
11/14 Romney 23, Cain 22, Gingrich 16, Perry 08 (Pew Research)
11/13 Romney 24, Gingrich 22, Cain 14, Perry 12 (CNN)
11/13 Gingrich 28, Cain 25, Romney 18, Perry 06 (PPP (D))
The first thing that the reader should notice is that Newt Gingrich has taken the lead. The second thing he should notice is that Gingrich is only slightly ahead of Mitt Romney. Romney is within the margin of error in some of the polls, and indeed is in first place in some of the polls taken a week ago.
Next, the polls clearly show Cain in third place, several points behind Romney and Gingrich. This leaves the impression that Cain is a spent force, doomed to decline. But Cain's strength is frontloaded in Iowa and South Carolina. Unless or until Cain falls even further, Cain remains a factor. Specifically, he's splitting the Anti-Romney vote with Gingrich.
Over the next few weeks, Elephant Watcher will be paying close attention to whether Cain falls into oblivion. If not, it could represent the Tea Party purists finding fault with Gingrich. Like Romney, Gingrich's conservatism may be called into question. The voters who don't care about electability may hold onto Cain. Those who simply want an Anti-Romney will show less resistance and will jump easily from Cain to Gingrich.
It should be noted that Gingrich's strength is overestimated in the national primary polls because he has not been attacked or vetted yet. Once he comes under the scrutiny of the media and the other candidates, his numbers are likely to fall. In mid-October, we explained some of Newt Gingrich's vulnerabilities. Voters have not taken these into account yet. By contrast, voters have already taken Cain and Romney's weaknesses into account. When a candidate reaches proper frontrunner status (as Romney, Perry, and Cain did earlier this year), all of his opponents will attack him during the debates. Only Romney managed to survive the vetting process, and now it will be Gingrich's turn.