One of the top Republican senators, Sen. John Thune (R-S.D.), announced Saturday he’s running for reelection after saying he wasn’t sure if he would. “I’ve always promised that I would do the work, even when it was hard, uncomfortable or unpopular,” Thune said in a statement. “That work continues, which is why after careful consideration and prayer, and with the support of my family, I’m asking South Dakotans for the opportunity to continue serving them in the U.S. Senate.” Thune, 61, is the Senate minority whip, making him the second-in-command of the Republican conference in the upper chamber and positioned to take the top post if Senate Minority Leader Mitch McConnell (R-Ky.), 79, steps aside at some point. Thune had been weighing retirement, but received public encouragement from McConnell to run for a fourth term. “It would be a real setback for the country and for our party if he …