As former Massachusetts governor Mitt Romney campaigns hard on the idea of building private businesses, a new Gallup poll finds that business owners are increasingly unhappy with President Obama.

President Obama tours a Master Lock factory. (JASON REED/REUTERS)

That’s a drop of 6 percentage points from the first quarter of the year, when 41 percent of business owners gave Obama a positive job approval. It was the only group that became significantly less approving of the president over the past three months.

According to Gallup the biggest drop was between March and April, and the poll was taken before Obama’s “you didn’t build that” comment. So this shift likely has more to do with economic indicators than former Romney’s attacks.

But it’s clear why Romney has latched onto that remark — business owners are a group already primed to be skeptical of the president.

Only 3 percent of working voters own their own businesses, but the group has symbolic power for both candidates as the engine of the economy and the group most attuned to economic change.

Across occupations, working Americans are divided on the president, with approval and disapproval tied at 47 percent. His approval went up significantly over the past three months with installation and repair workers as well as clerical and office workers. (The 13 point jump in Obama’s approval with repair workers is a reminder not to read too much into any one poll.)

Professionals, office workers and service industry workers are the groups most approving of Obama. Business owners; farming, fishing and forestry workers and construction or mining workers are the least.