When it comes to engaging people on Facebook, Sen. Rand Paul (R-Ky.) has some work to do. About 865,000 different people commented on, shared a note or otherwise engaged with the Kentucky lawmaker when he announced his campaign for the White House on Tuesday, according to Facebook. In all, Paul’s announcement generated a total of 1.9 million interactions — both positive and negative — during the day. By comparison, 2.2 million Facebook users talked about Sen. Ted Cruz (R-Texas) when he announced his campaign last month, generating a total of 5.7 million interactions. The metrics are just one sign of...