The most recent Republican presidential nominee, Mitt Romney, says he doesn’t think GOP front-runner Donald Trump will ever release his tax returns and believes that the billionaire businessman is hiding something significant.

In an interview with the Boston Globe, Romney also cites the main reasons he decided to give a blistering anti-Trump speech earlier this month. One was Trump’s call for not allowing Muslims into the U.S. But it was the interview on CNN in which Trump wouldn’t disavow David Duke and the Ku Klux Klan that Romney says spurred him to action.

Romney tells the Boston Globe that Trump’s recent remarks that Islam hates America are highly offensive and bigoted. He also says Trump represents a threat to both the GOP and the country.

Romney admits he has been wrong before about the 2016 presidential campaign. He says he didn’t think Trump would join the race and would quickly disappear if he did. He thought Trump’s disparaging comments about Sen. John McCain would cost him supporters. And Romney says he thought Jeb Bush would be the Republican nominee.

(AP)