Update, 1/21/08: John McCain's win in South Carolina has placed him in a strong position to win the Republican Party's nomination. However, he still faces an important obstacle: opposition from conservative leaders. I think this opposition could create an interesting dynamic over the coming weeks. Accordingly, I thought it worthwhile to republish this essay, which was originally offered last week.

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Since his win in New Hampshire, many have come to view John McCain as the Republican frontrunner. He has a lead in the RCP national average, and he is the favorite at InTrade's future's market.

I think this talk is a bit hasty. Most obviously, McCain and Romney are tied in Michigan - and the polls over the last three weeks have been largely conditioned by who has won. So, who knows how the Michigan results will influence South Carolina and the rest of the nation.

There is another reason I am hesitant about this bandwagon. I think that the problem that nearly destroyed his candidacy last summer is still there - and it could yet do him in. The problem? Conservative leaders do not care for his candidacy.

Before I get into this, I need to clarify a common misconception. Many people wrongly assume that average voters are as ideological as party leaders (broadly defined to include elected party members, prominent personalities in the party, and ideologues on op/ed pages and in opinion journals). They are not. In fact, the highest estimate I have seen for the percentage of the public that thinks ideologically is 30%. And many of those people think in an effectively ideological manner - e.g. they use the information they get from trusted opinion makers to formulate opinions on inter-related issues.

This means that McCain is probably more acceptable to rank-and-file Republicans than we might initially think. For instance, according to the New Hampshire exit poll, McCain won voters who identified themselves as "somewhat conservative," 38% to 35%. Romney won those who identified themselves as "very conservative," 43% to 18%. These results are consistent with the previous paragraph. Romney won the strong ideologues. McCain won the weak ideologues.

McCain's problem has more to do with conservative leaders than the rank and file. You probably have picked up on this impressionistically. National Review endorsed Romney. Rush Limbaugh has been openly critical of McCain's candidacy. Human Events is no longer the significant intellectual force it was three decades ago - but I thought it was telling that it endorsed Thompson after McCain won New Hampshire.

If you examined McCain only on paper, this would surprise you. By many metrics, he is the classic Republican frontrunner. He has been in Congress for more than 25 years. He was on Bob Dole's vice-presidential short list. He was the runner-up in the 2000 contest. He has a lifetime American Conservative Union (ACU) rating of 82.3. Above all, he has great credibility on two issues that will be important in November, the Iraq war and the war on terror.

Nevertheless, opinion makers do not much care for his candidacy. Apparently, neither does the Republican congressional caucus. Examining congressional endorsements for McCain and Romney, excluding in-state supporters (as they often act more out of home state pride than ideological proximity), we find some interesting results. 34 Republicans have endorsed Mitt Romney, while just 24 have endorsed McCain. Furthermore, Romney's supporters are more in line with conservative opinion. Their average 2006 ACU rating was 84.1, and 26 of them come from states Bush won in 2004. Meanwhile, the average 2006 ACU rating for McCain's supporters is 70.7, and just 12 of them come from Bush states. In light of McCain's résumé, this is consequential. He should have locked up most members of the Republican caucus, but he has not.

I believe that McCain's long-standing disagreements with conservative leaders could hurt him moving forward, just as it hurt him in the summer. One of his big problems is that viability is partially a subjective assessment. It has a complex relationship with likeability: people tend to view candidates they like as more likely to win the nomination, and they tend to like candidates the more they think they can win the nomination.

I think this contributed to the McCain "implosion" last July. The demise of his candidacy was quite overstated. Lots of campaigns have staff shakeups and money problems. But McCain's troubles were taken as a sure sign he was finished. I think that shows how likeability can affect viability. Conservative leaders were more inclined to write McCain off because they do not like him. They stopped talking about him, and the voters stopped considering him a viable alternative.

As we all know, McCain stuck it out - and New Hampshire delivered him a big win. He is now back at the top of the polls. But, I wonder whether he will once again be undone by the tense relationship with conservative leaders. I see two potential problems.

First, should McCain lose Michigan on Tuesday, he might be criticized more harshly than a mainstream conservative candidate would. Look, for instance, at Romney - who, despite having lost Iowa and New Hampshire, is still considered viable by many leaders. It is unlikely that McCain would enjoy that kind of charity should he lose Michigan or any subsequent state. This gives him a smaller margin for error.

Second, I think the prospect of a McCain nomination gives his mainstream opponents a wider margin for error. I do not think that McCain can end the nomination battle with wins in Michigan and South Carolina. Because conservative leaders dislike him, I think they might "rediscover" a viable alternative to him. Romney, Thompson, or even Giuliani could be brought back to life in a final effort to stop McCain. This would not happen if he was more acceptable to conservative leaders. Again, I think this is a big part of what is keeping Romney alive right now. No candidate in the modern era has made such a try for Iowa and New Hampshire, lost them both by wide margins, and gone on to win the nomination. The fact that many leaders are still holding out hope that Romney can win is, I think, a testament to how much McCain rubs them the wrong way.

By themselves, conservative leaders cannot stop McCain. The liberalization of the nomination process has left the upper echelons of both parties less able to determine directly who wins. However, they have indirect power. They can influence which candidates are seen by the voters to be credible candidates. Through their dialogue with one another as well as their direct communications to the public - they help establish voter expectations, and therefore the range of viable alternatives voters perceive. The more they talk up a candidate's viability, the more viable he becomes. The less they talk it up, the less viable he becomes. This is the power to set the agenda. Conservative leaders could help take McCain off the agenda if he falters, or they could help to place an opponent on the agenda to stop him.

Final point. Everything that has been written here applies to Mike Huckabee all the more. Huckabee is even more unacceptable to conservative leaders (he has the endorsement of only three out-of-state Republican members of Congress). His campaign even seems to be courting their contempt. McCain, to his credit, has worked hard since the immigration bill not to thumb his nose at conservative leaders. But not Huckabee. And I think that they would only accept Huckabee's nomination after he has won a majority of delegates. Until then, they'll find somebody, anybody to oppose him.