Like Mr. Obama, who said he could “probably do every job on the campaign better than the people I’ll hire to do it,” Mr. O’Rourke seems to suspect he’s the smartest man around. In his Senate race, he made a point of not hiring consultants or pollsters. He could pull that off in Texas—though he lost the election—but running for president is a bigger enterprise by orders of magnitude. To win, Mr. O’Rourke must build a team of smart people and listen to them. That requires leadership and management skills that may be beyond the reach of a punk-rock musician turned web-services small-business founder turned politician—unless he changes tack.

Mr. O’Rourke also had an advantage in Texas. Republican Sen. Ted Cruz inexplicably ignored him, largely letting Mr. O’Rourke define himself on his own terms for 17 months. Not until after Labor Day did Mr. Cruz really engage his Democratic opponent, ultimately beating him by 2.6 points. This time it will be very different: Mr. O’Rourke’s Democratic opponents already dropped opposition-research packets on him and sent allies to his events to ask uncomfortable questions and subtly criticize him for his shallowness and elusiveness on the issues. Watch for intraparty rivals to make a bigger deal soon of his past congressional apostasies, like means-testing entitlements and increasing Social Security’s eligibility age.