The official Democratic group working to saving the party’s Senate majority is going back on the air to provide a late boost to Alison Lundergan Grimes, the Kentucky Democrat trying to throw out Senate Minority Leader Mitch McConnell, a week after the group shocked political observers by appearing to pull out of the race. The Democratic Senatorial Campaign Committee will reserve $650,000 in advertising, according to a DSCC official, who said that internal polling shows undecided voters turning to her. A week ago, it appeared that Grimes would be left on her own as she entered the home stretch of the race with the DSCC going dark in Kentucky.