Mitt Romney wants you to know that he used to be a successful businessman, and that his managerial experience could help revive America’s sputtering economy. It’s a message that has resonated with many of his former private sector colleagues, who are expected to shower Romney with campaign contributions once again. But they should be careful what they wish for. The further Romney progresses in his campaign, the greater the scrutiny on his own supporters.

Romney’s resume is no secret, but he doesn’t itemize it on the campaign trail. Perhaps that’s because explaining his evolution from management consultant to venture capitalist to private equity executive would sound more Wall Street than Main Street.

Venture capital, of course, is a job creator. Private equity, on the other hand, is a mixed bag — something Romney himself has admitted: “Sometimes I was successful and helped create jobs, other times I was not.” And more of Romney’s financial support has come from the mixed bag. In 2007, private equity execs donated around $5 to Romney for every $1 from VCs.

Some of that support may be more about personal relationships than politics, but many buyout executives believe that President Romney would be a boon to their industry — vetoing increases to the capital gains tax rate or any proposal to change the tax treatment of carried interest (firm profits). In their minds, he’d support energy-focused firms that want to drill, baby, drill, while also publicly acknowledging the need for clean technologies into which other PE shops have sunk billions of dollars. Plus, President Romney probably wouldn’t be on the labor union Christmas card list. What Romney’s private equity backers ignore, however, is that it’s a long road to the Oval Office. The “businessman” minimalism won’t last forever and, when it gets scrutinized, all of private equity will be on national trial.

To be sure, that is unlikely to happen during the Republican primary. Any criticism of private sector experience by his opponents could be misread as an implicit endorsement of the public sector; the only time Bain Capital came up during the 2008 primaries was when Mike Huckabee suggested that the firm’s investment in radio giant Clear Channel — made long after Romney left — was an explanation for Huckabee’s inability to secure endorsements from some of Clear Channel’s conservative talk show hosts.

But if Romney wins the Republican presidential nomination, the gloves come off. For a preview, recall what Obama campaign aide David Plouffe said in August 2008, when Romney was a front-runner to become John McCain’s running mate: “This is someone who was a job-killing machine in business … He’s someone who has been proficient at using tax havens in places like the Cayman Islands that Americans have become increasingly tired of.”

It’s the same playbook Ted Kennedy used to defeat Romney in a 1994 U.S. Senate race — one that featured television ads of laid-off workers from a Bain Capital portfolio company. And it’s bound to be effective, not just in hurting Romney, but in hurting private equity at large. This is an industry whose wealthy senior professionals pay most of their taxes at a lower rate than teachers pay. An industry in which firms can make money on an investment even if the company goes bankrupt on their watch. An industry that has hurt plenty of people, despite credible arguments that it’s been a net benefactor.

Perhaps we’ll hear about big-name, private equity–backed retail bankruptcies, like KB Toys or Linens ‘n Things. Or recent accusations — largely unfair — that Blackstone pushed a chain of British nursing homes to the brink of collapse.

Perhaps that is an acceptable tradeoff for Romney’s private equity backers: short-term pain for long-term gain. But they had better be sure. Because if Romney wins the nomination and loses to Obama, only the pain will be left. And the regulatory consequences that are born of national outrage.

This article is from the July 25, 2011 issue of Fortune.