Philip, I certainly agree with you -- and with a couple of Spectator readers -- that at this point, Bob Barr's Libertarian candidacy appears to have done no significant damage to John McCain. And you are also right that a Barr bid for the Ron Paul vote does nothing to attract those conservatives (e.g., Rush Limbaugh) who are disgruntled mainly because of McCain's "maverick" departures from Reaganite orthodoxy. A cynic might suspect that the chief political object of Barr's appearance at Monday's let's-talk-to-Iran rally was to convince Paul's anti-war backers (and especially Paul's donors) that Barr is "one of them."
If that were the only thing that Barr were doing -- if he were a single-issue anti-war candidate -- then there would be no prospect that he would ever make any headway among disgruntled Republican conservatives. However, Barr is also reaching out to mainstream free-market groups like Americans For Prosperity, and will appear at an event in Marietta, Ga., next week during AFP's hot-air balloon tour. An AFP official pointed out to me yesterday that John McCain was a co-sponsor of the Lieberman-Warner cap-and-trade bill that failed on a cloture vote last week.
To give you an idea of how Barr might make his pitch to disgruntled Republicans, look how he goes after GOP leadership in response to a question (1:55) during this interview with Bloomberg: