The biggest obstacle faced by those who are trying to build (for whatever reason) the case that Mitt Romney has already pretty much won the presidency is his consistently poor favorable-unfavorable ratings. Even in a recent poll where he was running even with the president–last week’s CBS/NYT survey–his favorability rating was underwater.

Nate Silver of FiveThirtyEight took a long look this week at the relationship of favorability and election outcomes in the past. And the fairly clear answer from his data is that Mitt’s poor standing isn’t necessarily a sign of doom this far out, but if it persists late into the campaign he’s got a real problem.

Overall…early-stage favorability ratings have had a mixed track record as a predictor of election outcomes. The candidate with the better net-favorable rating in the early-going won the election in 1976, 1980, 1984, 1996, and 2008. But Mr. Clinton won the election in 1992, despite making a poor first impression on voters. On the flip side, Michael Dukakis had very promising favorability numbers early in the 1988 cycle, but they deteriorated over the course of the election cycle and he took a clear defeat. (I’m not sure where you’d classify the 2000 election because of the split between the popular vote and the Electoral College, or 2004 since George W. Bush and John Kerry had essentially the same net favorability rating in the early going.)…

If we look at favorability ratings in the late stages of a presidential race, however — as measured by an average of New York Times/CBS News polls conducted from September of the election year until the election date — we find a much stronger relationship. Although there is not data on this for 1976, the candidate with the stronger net-favorable rating in the late stages has won every election since 1980, and there has been an almost-perfect correspondence between the margin of the favorability gap and his margin of victory or defeat in the popular vote.

Mitt’s favorable/unfavorable ratios actually are improving right now, for the fairly obvious reason that conservatives aren’t hearing negative messages about him from his primary rivals. This will continue to give him a modest life, but to get and keep his numbers in a positive range, he’s eventually going to have to start showing some personal appeal to people outside the universe of Republicans and Republican-leaning independents.

You don’t have to be likable to become president, as Richard Nixon proved for all time. But it really does help, and we will soon be watching–with interest, and perhaps amusement–Team Mitt’s efforts to boost his regular-guy credentials, hard as that will be.

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Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.