The knives are already out for him.
O'Rourke was one of the very high-profile Democrats ahead of the 2020 election cycle. That means opposition research groups have already been hard at work looking to dig up dirt on him in any way they can.
During his time in Congress, O'Rourke had a fairly moderate voting record, which conservative political groups could use to highlight areas he has at times been less liberal and steer the Democratic base to sour on him.
If he does run, he's showing up late.
At least 11 Democratic candidates have already started their campaigns, all announcing before Republicans had jumped in at the same time in 2015.
Joining the 2020 race allows candidates to capitalize on some momentum and boost small dollar donations from the immediate hype.
But the later a candidate waits, the more ground and momentum they could be ceding to other eager Democrats already traversing the early primary states.
He's young.
There have been a handful of presidents elected before they turn 50, but it is exceedingly rare. Meanwhile, the field of Democrats features a handful of older candidates with lengthier résumés.
He's already been profiled by almost all the major magazines.
If you have read a profile of O'Rourke in a glossy magazine in the past year, you would have to be a lot more specific about which publication wrote it.
O'Rourke got the full treatment during his Senate race in 2018, becoming the subject of nearly a dozen magazine profiles in publications like Esquire, TIME, GQ, Vanity Fair, The New York Times, Politico, and more.
These profiles help elevate candidates on the national stage. When there are already so many on the books, it makes it unlikely he will get another.
He is fresh off a loss.
O'Rourke narrowed the gap with incumbent Republican Sen. Ted Cruz in the 2018 Texas Senate race. But he failed to unseat Cruz, who has typically been a very polarizing figure on the right.