COLLINSVILLE, Illinois — Mitt Romney began three days of campaigning ahead of Tuesday’s Illinois primary with a sharp attack on President Obama and a defense of his own wealth and success.

 At a Saturday evening town hall meeting, the frontrunner in the Republican presidential race opened by seizing on rising gasoline prices and accusing the president of having come to office favoring policies designed to drive them up.

 Calling the president an “economic lightweight,” Romney said Obama has undergone an election year conversion on the issue of gasoline prices in response to the public anger and political damage the increases have caused.

Romney accused three administration officials—Energy Secretary Steven Chu, Interior Secretary Ken Salazar and Environmental Protection Agency Administrator Lisa Jackson— of working to push up energy prices. He said they should either resign their offices or be fired by the president. 

The former Massachusetts governor got mostly friendly questions from the audience. But one man, holding a video camera, asked Romney about his personal wealth and investments. Romney said the questioner had his facts wrong and explained that his investments are held in a blind trust. 

He ended the event with a defense of his business success, which has helped him amass a huge personal fortune. “I am not in this race to make money,” he said to rising cheers from the audience. “I’ve already made enough… I’m not embarrassed about being successful, but I’m embarrassed for people who think there’s something wrong with that.”

 Romney did not mention rival Rick Santorum by name, but a day ago he said the Republican Party should not make the mistake of nominating an economic lightweight to go against Obama. 

Romney campaigned in Collinsville after starting the day in Puerto Rico, which holds its GOP primary on Sunday.