The Washington Post says McCain should be afraid:
Sen. John McCain is champing at the bit to run against Sen. Barack Obama in the fall. But while the presumptive GOP nominee focuses on his likely Democratic rival, he should also worry about his own right flank. Bob Barr entered the presidential race last week as a Libertarian, in time for that party's nominating convention (which starts Thursday), and while the former Republican congressman from Georgia isn't going to become president, his run is no joke. Barr might well inherit the sizable support garnered by Rep. Ron Paul during his own run for the Republican nomination -- and leave McCain sputtering the sorts of epithets usually uttered by Democrats talking about Ralph Nader.
I don't buy it. Ron Paul voters would seem to be the irreconcilables of the Republican party. They aren't going to vote McCain no matter what, but they might have voted Obama to punish their party and force a withdrawal from Iraq. If Andrew Sullivan is any indicator, supporting Ron Paul and Barack Obama are not mutually exclusive. In the absence of a third party run by Paul, or a Libertarian bid by Barr, these voters would have ended up in the Obama column. Instead we may have four anti-war candidates on the ballot--Obama, Nader, Paul, and Barr. And whatever protest vote exists within the Republican party is minuscule compared to the Democratic protest vote against Obama (see West Virginia, Kentucky, Ohio, Pennsylvania, etc.).
Barr will give anti-war voters who bitterly cling to guns and religion another option in November. If he has any impact at all, and he may not given the nature of his early attacks, he seems likely to siphon votes from Obama, not McCain.