Mr. Romney, a former Massachusetts governor who is considered the front-runner for his party’s presidential nomination, came and left the boarded-up factory within 10 minutes, after making a brief statement and fielding a handful of questions.

“I didn’t pick this spot; he did,” Mr. Romney said, in a reference to Mr. Obama’s 2009 speech at the same location. “This is the spot he picked to symbolize the success of his stimulus, and my eyes tell me it ain’t working.”

Mr. Romney has continually attacked Mr. Obama’s handling of the economy, but on Thursday he said the president wasn’t causing harm. “I didn’t say things are worse,” he said in response to a reporter’s question. “It’s that the economy hasn’t turned around.”