Senate Republican strategists are increasingly worried that the near absence of TV ads from Donald Trump’s campaign in key battlegrounds will do irreversible harm to already difficult races.

In state after state with both a presidential and Senate race, Hillary Clinton and her allies are on pace to spend tens of millions of dollars more than Trump and his supporting super PACs, according to political operatives tracking the data.

Unless the GOP presidential nominee dramatically increases his spending, the gap will be downright gargantuan some places. In North Carolina, where Republican Sen. Richard M. Burr faces a tough re-election fight, Clinton and Democratic groups are on track to spend $21 million. That’s seven times more than Team Trump’s $3 million.

[Senate GOP Super PAC Makes Big Push in North Carolina]

GOP strategists say that at a time when voters are splitting their tickets less than ever, Clinton’s on-air barrage could inflict significant damage on the party’s reputation as it fights to save its slim Senate majority.