Barr is a dud. He's arrogant. Probably a bigot. Not the brightest bulb IMO.
Your contention that Barr's votes are coming from "McCain's base" doesn't appear to be supported by the facts. Libertarians are not Republicans. Then there is this:
The battle for the presidency also includes some minor party candidates, including Independent Ralph Nader, Libertarian Party candidate Bob Barr, and Green Party candidate Cynthia McKinney — but the poll suggests they don’t have any impact on the shape of the race.
When they are added to the equation, the race between McCain and Obama remains tied, at 45 percent each, with Nader and Barr at 3 percent each and McKinney at 1 percent.
http://politicalticker.blogs.cnn.com/2008/09/08/cnn-poll-race-dead-even/#more-17569
3% isn't relevant? It appears quite a few GOP folks believe it is.
Bob could be the Ralph Nader of 2008," said
Dan Schnur, a GOP consultant in California who worked on McCain's 2000 campaign but is not involved in this year's contest. Consumer advocate Nader is the third-party candidate many Democrats blame for helping George W. Bush narrowly win in 2000.
Rep. John Linder, a Republican who defeated Barr in 2002 after Georgia's Democratic-controlled Legislature redrew congressional boundaries to put the two lawmakers in the same district, said he didn't think Barr would top 4 percent of the vote.
"But in some states that may be enough," Linder said."I think John McCain is going to have to battle for Georgia, a state that was a gimme for George Bush," said
Matt Towery, a former Republican state lawmaker in Georgia who runs a political media company.