Rick Santorum ended his bid for the Republican presidential nomination yesterday, making Mitt Romney the all-but-certain nominee. Newt Gingrich and Ron Paul are staying in the race, but now attention is shifting to Romney’s future choice of a running mate and uphill battle to replace President Obama. Speculation that Santorum would quit the race rose after his three-year-old daughter, Bella, had to go to the hospital over the weekend. She suffers from Trisomy-18, a rare disorder that is fatal for all but one percent of its victims by age 10. She has been released from the hospital, but the decision...