Gallup says that not having a clear presidential front-runner in the Republican party is historically abnormal:
“The wide-open battle for the 2012 Republican presidential nomination — with nearly a three-way tie among Mike Huckabee, Sarah Palin, and Mitt Romney — is quite different from the typical pattern observed in past Republican nomination contests. In Gallup polling since 1952, Republican Party nomination races always featured a clear front-runner at this stage of the campaign, and in almost all cases, that front-runner ultimately won the nomination.”
It’s worth noting, however, that much of this chart is ancient history, when GOP candidates had names like “Romney” and “Bush.”
On a slightly more serious note, observe how many second-place candidates ended up not seriously competing for the nomination: Ford never formally declared in 1980, Dan Quayle never made a serious bid in 1996, citing health issues; Elizabeth Dole ended her run before any of the primaries in 2000. Some might argue that Rudy Giuliani’s run turned out to be not-so-serious last cycle.