But the most-likely scenarios for Deval Patrick’s entry into the race are, in descending order of probability:

(1) He flashes and fades quickly, like Fred Thompson in 2008 or Rick Perry in 2012, and never makes a significant impact in actual primary voting.

(2) He siphons off enough voters in New Hampshire to either ruin some other candidate’s day or to render the result such a muddle that there is no clear winner and any momentum from Iowa is blunted in the Granite State.

(3) He builds enough support to do well in South Carolina, which creates enough of a splintering that the Democratic race becomes a long slog to the convention—with the real possibility of no candidate amassing enough delegates for a first-ballot nomination.

(4) He gives an impressive performance in debates, doesn’t create a viable coalition, and becomes an attractive vice presidential pick for the eventual nominee.