The Elephant Watcher profile of Ron Paul reveals that he has many weaknesses. Paul is arguably the weakest candidate in the field; he is not given a high rank on any of the three candidate attributes (perceived conservatism, perceived electability, and rhetorical skill). Paul also lacks any geographical advantage that might help him win an early primary. Accordingly, Elephant Watcher has calculated that Ron Paul's odds of winning the Republican nomination are 0%.
The polls of early primary states demonstrate the extent of Paul's challenge: He has failed to place first or second in any poll in any state. He does, however, manage third place in some New Hampshire primary polls. Paul tends to poll well, considering his handicaps. However, his numbers never increase, and they reflect his enthusiastic--but static--base of libertarian support. Paul's numbers are healthy enough to ensure that he will be invited to primary debates for a long time to come, whether the debate sponsors like it or (more likely) not.
What about the 2008 vs. 2012 comparison? In some ways, Paul is better off now than he was four years ago. He has greater name recognition, and he has the benefit of experiencing a presidential primary. His support among libertarians has not diminished. Instead, he has been branded as the "official" libertarian. Gary Johnson, the former governor of New Mexico who was only invited to the first debate back in May, was quickly shuffled aside in favor of Paul. One of Paul's greatest weaknesses, his opposition to American intervention abroad, has been mitigated by the general unpopularity of the wars in Afghanistan, Iraq, and Libya. It is not shocking to hear a Republican candidate say the troops need to begin returning from Afghanistan.
By and large, Paul's weaknesses from 2008 remain. As Paul learned during the Republican primary debate on September 12th, conservative audiences still boo if you claim American foreign policy caused the 9/11 attacks. But Paul's more fundamental problem is that he doesn't care what Republicans think or feel. He has little strategy at all, though his occasional criticisms of Rick Perry appear to be prompted by campaign advisors. Otherwise, Paul's campaign actions are random. Paul's lack of strategy is likely a result of his understanding that he cannot win the nomination.
Since Paul is viewed as unelectable while simultaneously alienating most Republicans, he will always be limited to a small, core group. Many of the primaries will not award delegates on a winner-take-all basis, so Paul will be able to amass some number of delegates. If the primary goes all the way to the convention, one can count on Paul taking the opportunity to make noise. Like his campaign, the noise will have little impact.