Former Republican congressman Robert Barr of Georgia recently announced he is running for president as a Libertarian. This is a formidable development, and it's by no means out of the question that Barr could attract enough otherwise conservative voters to defeat John McCain and put Barack Obama in the White House.

Of course, Obama has his own problems with possible rivals on the left side of the political spectrum. That hardy perennial Ralph Nader has already made it clear that he intends to run, and while he may be old news, even a poor showing by Nader on Election Day might be enough to tip the scales to McCain in a close-fought election. But Barr is much the fresher face, and it is only prudent to assume that he would attract more votes than Nader.

As the presidential candidate for the Libertarian Party, which has near-total ballot access, Barr would possess an asset available to neither Nader nor Pat Buchanan in their own recent independent runs for the Oval Office. Assuming Barr gets the Libertarian Party nomination at its convention later this month, he will be on the ballot in most if not every state come Election Day.

Barr, therefore, is a serious problem for McCain. As a congressman from Georgia in the 1990s, he racked up an impressive record as a social conservative, and, since retiring, he has waged a steady battle against what he sees as the Republican Party's determination to use the Patriot Act and other weapons to weaken the Bill of Rights. As he recently told The American Conservative, "I decided that whatever years the Lord leaves me on this earth, I was not going to waste them remaining involved with a party that had no interest in individual liberty." So it's goodbye GOP, as far as Barr is concerned.

In terms of issues, Barr identifies "the proper role of the government in the economy and the scope of government spending" as the key problem. But he hastens to add that Iraq is also important: "$400 million a day is a lot of money that could be better utilized by American citizens to do the things here at home." So he opposes the war in Iraq, too.

And he is equally dubious about confronting Iran. "I think we ought to remove from the table some sort of significant military operation against Iran. That would be very irresponsible and not likely to offer any degree of success." Instead, "I think the United States needs to deal with the government in Iran as a professional government" -- meaning, presumably, by diplomatic means.

Conservative Republicans may have serious reservations about some, or even all, of Barr's positions, but there is no denying that many of them appeal to conventional conservative doubts.

So it seems very likely that, come November, conservatives will find on their ballots not only the names of McCain and assorted liberals but that of a staunch fellow conservative resolutely opposed to big federal spending and military involvement in the Middle East. Most will realize, of course, that Barr has no chance whatsoever of actually becoming president. His role, therefore, is inevitably that of a spoiler -- a person whose only serious function might be to put Obama in the White House. That will be more than enough to turn most conservative voters against him. But a few -- perhaps a dangerously sizeable few -- will vote for Barr.

Barr, of course, knows all this, and he admits that his real hope, strategically, is "to strengthen the ability of the Libertarian Party to be a permanent, viable force in American politics."

Which is all very well, but it's a high price to pay for four or eight years of Obama as president of the United States.