A day doesn’t pass without some TV pundit or political “strategist” furrowing his or her well-groomed brow and referring knowingly to the mythological “Republican base.” Everyone’s talking about the GOP base, but not all the talking heads are referencing exactly the same thing. Looking at caucus and primary returns thus far, I’m not convinced that most definitions of the “base” are accurate, nor that the supposed influence of the base is as great as some allege, particularly in the current presidential election cycle.

Some commentators invoking the concept of the base are simply making a broad reference to self-professed “conservatives.” Others are invoking a narrower band of Republicans whom we once called “movement conservatives” — voters who are devoutly and consistently conservative across a disparate range of issues; taxes, abortion, guns, commies, etc. Often, Democratic pundits and strategists, for nefarious purposes, seem to define the Republican base even more narrowly as evangelical Christians or the religious right. Or, alternatively, they trivialize our base as Wall Street billionaires.

As I struggle for a definition of “the base,” I would suggest that it might best be defined as Republican voters likely NEVER to vote for a Democrat, under any circumstances. In light of that definition, it’s interesting that the candidates getting the most votes so far in Republican caucuses and primaries are being supported by voters who might well vote for Democrats. A lot of voters backing front-runner Sen. John McCain (Ariz.) are very independent-minded individuals who easily might consider voting for a similarly maverick candidate like Sen. Joe Lieberman (I-Conn.). Dare we call these Lieberman Republicans?

Mike Huckabee’s core backers are Republican Christians with a strong populist streak, some of whom might vote for the right Democrat. Many of these voters fa­vored another Arkansan, Bill Clinton, when he challenged the patrician, pro-business George H.W. Bush in 1992. While Clinton’s philandering and liberal social views eventually alienated most of these voters, I’ll call them Early-Clinton Republicans.

Rudy Giuliani is trying to climb back into the race, and his entire campaign seems premised on the notion that he’ll attract Democrats. Thus I will suppose that the voters he’s courting in Florida during the coming week are similarly not-so-partisan in their vote behavior. They’ll occasionally embrace a Democrat, just as Republican Giuliani endorsed liberal Democrat Mario Cuomo over George Pataki in a 1994 New York gubernatorial contest. We’ll call these Cuomo Republicans.

Even some of the donors bankrolling Mitt Romney, particularly the Bain Group alumni financiers raising gobs of money, are non-ideologues who would vote for a Democrat once in a while. In Michigan, Romney’s only significant victory, it is certain that some of his “Republican” supporters also backed either Democratic Gov. Granholm or Michigan Sen. Debbie Stabenow in the last decade.

In reality, however, Romney has done well with “base Republicans” if we define them as voters who’ll never vote for any Democrat.

Looking ahead to November, these observations about the primaries provide fresh ammunition to those who want to challenge Karl Rove’s central strategy premise of organizing general election campaigns around arousing “the base.”

The Republican base may be too small and fragmented to provide a firm foundation for victories.

It’s encouraging that GOP front-runners McCain and Huckabee might attract ticket-splitters and conservative Democrats should they win the nomination. Some other Republicans in the race might find it tough to woo these crucial swing voters. The base-only candidates would make good running mates, but shouldn’t lead the ticket.

Hill is director of Hill Research Consultants, a Texas-based firm that has polled for GOP candidates and causes since 1988.