She asked Mr. Cohen a series of specific questions about how Mr. Trump had handled insurance claims and whether he had provided accurate information to various companies. "To your knowledge," she asked, "did Donald Trump ever provide inflated assets to an insurance company?" He had.

She asked whether Mr. Trump had tried to reduce his local taxes by undervaluing his assets. Mr. Cohen confirmed that the president had also done that. "You deflate the value of the asset and then you put in a request to the tax department for a deduction," Mr. Cohen said, explaining the practice. These were the sort of questions, and answers, the committee was supposed to elicit. Somehow, only the newer members got the memo.

Ms. Ocasio-Cortez continued, asking, "Do you think we need to review financial statements and tax returns in order to compare them?" She pressed Mr. Cohen for the names of others who would be able to corroborate the testimony or provide documents to support the charges. In response, Mr. Cohen listed the executives Allen Weisselberg, Ron Lieberman and Matthew Calamari -- names that, thanks in part to Ms. Ocasio-Cortez, we will probably hear more about in the coming months.

These questions were not random, but, rather, well thought out. Like a good prosecutor, Ms. Ocasio-Cortez was establishing the factual basis for further committee investigation. She asked one question at a time, avoided long-winded speeches on why she was asking the question, and listened carefully to his answer, which gave her the basis for a follow-up inquiry. As a result, Mr. Cohen gave specific answers about Mr. Trump's shady practices, along with a road map for how to find out more. Mr. Cohen began his testimony calling Mr. Trump a "con man and a cheat"; In just five minutes, Ms. Ocasio-Cortez actually helped him lay out the facts to substantiate those charges.