I’m asked if it really is too late for any other Republican candidate to announce a presidential bid.

Right now, any sudden addition would have to run as a write-in candidate in a slew of early-voting states, making the odds of success exceptionally difficult. Filing deadlines for primary ballots have passed in Florida (October 31), South Carolina (November 1), Missouri (November 22), and New Hampshire (October 28). Because caucusgoers in Iowa write in the names of their preferred candidate, there is no filing deadline, but going from unannounced on December 1 to winning a significant share of the vote on January 3 is an exceptionally steep hill to climb.

Even if some late entrant were to do relatively well in Iowa, they would have to somehow sustain that momentum with write-in votes in three of the next big contests. Ask Rudy Giuliani how easy it is to keep a presidential campaign going without any delegates from New Hampshire, South Carolina, or Florida.

A few more filing deadlines are coming up soon: Tennessee’s is December 6 at noon; Oklahoma’s is the following day. The filing deadline for Louisiana and Michigan is December 9. Texas’s is December 15; Virginia’s is December 22.