WASHINGTON (AP) — President Donald Trump is prematurely claiming he proved naysayers wrong in boosting U.S. economic growth.

Speaking at events Thursday in Iowa and Illinois, Trump claimed victory in advance of Friday's government release of quarterly gross domestic product data, saying "nobody thought we were going to be this good" and that when he became president, "those numbers were bad."

In fact, the skepticism from economists has centered more on whether strong GDP growth would be sustainable after a few quarters. That question has yet to be answered; it's not unusual for the economy to...