When he’d have to decide: O’Rourke has the tightest timeline of the bunch. The filing deadline to be a candidate in Texas is Dec. 9, 2019, which is before any primary votes are cast.

The early-voting states — Iowa, New Hampshire, South Carolina and Nevada — have their primaries in February. On March 3, 14 states hold their primaries in what’s known as Super Tuesday. Some Democratic strategists think by then we could know who the nominee is. (Of course, the 2016 Democratic primary went all the way to June.)

His challenges: Democrats have already recruited someone, Air Force veteran MJ Hegar, to challenge Cornyn. She lost her 2018 congressional race but earned national attention for her strong campaign ads. She’s not as well known as O’Rourke in the state, but would Democrats be willing to switch allegiances if he got in the race?