Commenter “Davis X. Machina” asks: “What’s the absolute latest a candidate can realistically get into a presidential race? Not ballot-deadlines-latest, but real-world.”

Great question. During the last cycle, numerous pundits talked up a late entry in the Republican nomination contest well into fall 2007, when it was clearly too late. So what’s the real answer? Unfortunately, the best answer is a big, “it depends.”

I can do a little better than that, though. The invisible primary for 2016 began, on the Republican side, at approximately the same time that Karl Rove was having that Election Night tantrum on Fox News — although I suppose that Republicans who believed the aggregate polls may have started a few weeks earlier. On the Democratic side? The incumbent president’s party begins its jockeying for the next nomination some time during his first term. The invisible primary continues until the actual voting in Iowa and New Hampshire approaches, in this case at the beginning of 2016.

At some point in that long process, party actors begin to make commitments, and eventually settle on one or more finalists. Other competitors are winnowed out de facto (Democrats Joe Biden, Bill Richardson and Chris Dodd all made it to Iowa in 2008 but only after having long since lost any chance of winning), or formally (Republicans Tim Pawlenty, Haley Barbour and John Thune in 2012, the latter two of whom did some candidate-like things but never officially entered the field).

So when is too late? There are two key variables. One is the point at which party actors have moved from auditioning the prospects to actually deciding. That may happen as early as two or three years before the election, which appears to be happening among Democrats right now. Or it may take until the late fall or early winter entering the election year.

The other variable concerns potential candidates. During the invisible primary, potential candidates introduce themselves to party actors and demonstrate their fealty to the party’s policy positions, their capacity for running a national campaign and the skills and abilities that promise to make them reliable presidents. They also begin to demonstrate that they can attract enthusiastic support from party voters (before the actual primaries and caucuses), and that they would make solid general election candidates. But not all candidates begin at the same starting line. Hillary Clinton had already achieved pretty much everything on the 2016 nomination checklist by November 2012. By contrast, Massachusetts Governor Deval Patrick, and Maryland Governor Martin O’Malley, have a lot more to do. The more a candidate must achieve, the more time it will take to do it.

So the more open the nomination is, the longer the window for a candidate to enter the fray. Likewise, the stronger a given candidate is (think Clinton), the longer that candidate can wait to begin campaigning.

In this presidential election cycle, the Democratic side looks pretty settled already. Unless Clinton drops out or encounters unexpected turbulence, it’s already pretty late to enter the nomination contest except for the very heaviest of heavyweights. The Republican side, on the other hand, still seems fluid. In addition to candidates such as Rand Paul, Ted Cruz, and Rick Perry, who are actively campaigning, there is a large number of quasi-candidates — Mike Pence, John Kasich, Rob Portman — straddling the line between almost in the race and really in. I suspect that a candidate who hasn’t done some preliminary work would have difficulty catching up to the pack at this point, but it’s probably not too late for a plausible candidate to start from scratch. However, the window is closing. At some point in the next several months, Republican party actors are going to move from window-shopping to committing.

[Cross-posted at Bloomberg View]

Jonathan Bernstein

Jonathan Bernstein is a political scientist who writes about American politics, especially the presidency, Congress, parties, and elections.