PHILADELPHIA — John Fetterman continues to lead Mehmet Oz in the polls, but the Pennsylvania Democrat’s Senate campaign is privately sounding the alarm that things could change if he continues getting outspent on TV. In an internal memo on Tuesday to big-dollar donors, Fetterman campaign manager Brendan McPhillips warned that Oz and his Republican allies are together investing more in television ads than Fetterman and Democratic super PACs that support him. “I am writing with a wake-up call,” said McPhillips in the message, which was obtained first by POLITICO. “In the last three weeks alone, Republicans have spent nearly $12...