Increasingly pointed attacks on Mitt Romney’s work at Bain Capital may be resonating, but his private sector experience continues to be a key advantage to the Republican front-runner, according to the new Washington Post-ABC News poll.

Since December, there’s been a nine percentage point increase in the number of Republicans and GOP-leaning independents holding unfavorable views of Romney’s work buying and restructuring companies. Still, his corporate history remains a net positive, with a 51 percent majority seeing this work in a favorable light, far more than the 29 percent seeing it unfavorably.

In a separate question, by nearly 2 to 1, 50 to 28 percent, more say that his work as a corporate investor did more to create rather than cut jobs.

Nonetheless, the rise in unfavorable ratings among certain Republican groups is notable, although still limited. In the GOP base, 34 percent have negative impressions of Romney’s private sector work, up from 20 percent last month.

Those negative shifts in the Republican base are driven by the less conservative groups. Unfavorable ratings of Romney’s work are up 15 points among “somewhat conservatives” as well as those who “somewhat” support the tea party movement.

Wealth plays a role too. A third of Republicans with less than $75,000 in family income see his work unfavorably, up from 21 percent in December. Wealthier Republicans remain more favorable of his corporate work.

The attacks on Romney’s corporate past coming from his GOP opponents may be setting up similar arguments from the Obama campaign should Romney secure the Republican nomination.

By a wide 55 to 35 percent margin, more see economic unfairness as a bigger economic problem than over-regulating the free enterprise system.

Nearly six in 10 Republicans highlight government over-reach as the larger problem, while nearly eight in 10 Democrats see unfairness as a bigger issue. Among independents, 52 percent are more concerned with unfairness favoring the wealthy; 38 percent with interference with the free market that stunts economic growth.

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