David Prior, who was brought in to lead the Care Quality Commission in January after it faced criticism for failing to protect vulnerable patients, said that almost half of hospitals were now providing care which was either poor, or "not terribly" good.
He said the CQC had found 45 hospitals with problems dating back five years, and vowed that from now on regulators will take a "much clearer" approach in advising which hospitals should not be allowed to continue as they are.
We will be outside the system and the politics - we will have a huge role in the reconfiguration debate because we are independent.
More top news
The presumptive Republican nominee was speaking to a crowd in San Diego's convention centre, whilst 1,000 people demonstrated outside.
There will be sunny spells for many but heavy showers will spread across the UK in the afternoon.
Children's Commissioner review found 28% of children in need of support were sent away because their illness was not deemed serious enough.