WASHINGTON (AP) — Mitt Romney, the 2012 GOP presidential nominee and incoming Utah senator, has quickly set himself apart from other Republicans in the new Congress with a blistering attack on President Donald Trump's leadership and character.

Romney put to rest expectations that he would take his time getting his footing in Washington. Instead, in a Washington Post column published two days before Romney was sworn into office, he said Trump's "conduct over the past two years, particularly his actions last month, is evidence that the president has not risen to the mantle of the office."

Trump,...