Beto O’Rourke and his advisers are sending strong signals that he’s on the brink of announcing a run for president, a move that would conclude a months-long period of public and private introspection and alter the complexion of the crowded 2020 Democratic primary field. O’Rourke’s possible candidacy has been one of the most widely anticipated, following the enthusiasm he generated in a failed run for U.S. Senate from Texas, to the frustration of other hopefuls in a formidable field who note that he’s a former three-term congressman who lost his only attempt to win statewide office. By design or accident,...