With an opening on the Supreme Court looming, a major consultant past administrations once used to help vet nominees is back at the table -- after it was barred from the process the last two times under George W. Bush

The American Bar Association, which Bush brushed aside amid criticism that it had moved too far to the left, announced it had been welcomed back into the fold shortly after President Obama's inauguration. 

There are still questions, though, about the group's objectivity. And as Obama begins to narrow the field of potential nominees to replace Justice David Souter, conservatives are sure to watch closely the signals from the ABA. 

"The Standing Committee does not consider a potential nominee's ideological or political philosophy," the group said in a statement after Obama's inauguration. 

But a new study suggests that's not true. 

The findings compiled by three Georgia universities show that from 1985 to 2008 the most liberal nominees to the federal appellate bench had a 62.3 percent chance of getting a "well-qualified" rating from the ABA, while conservative nominees had only a 35.5 percent change of earning the same rating. 

"We were fairly surprised that we actually found such robust findings of this bias against conservative nominees," said Amy Steigerwalt, one of the lead researchers, with Georgia State University. 

For many conservatives the study was merely proof of what they had long believed. 

"I think now that the ABA has been unmasked as just another liberal special interest group, conservative senators ought not to take their word for anything more than that," said the Heritage Foundation's Todd Gaziano. 

"I think we've had some notable examples in the past where they have really played politics ... especially with Supreme Court nominees," said Sen. Orrin Hatch, R-Utah. 

But ABA supporters say they're excited to see the organization returning to its former role, and claim the study out of Georgia proves only one thing -- that Republicans nominate less qualified candidates to federal judgeships. 

"It's surprising that even some of these Bush nominees got the kind of passing marks that they did given that their qualifications were so scanty and weak frankly," said Nan Aaron, president of the Alliance for Justice. 

The clearest example of how much an ABA vetting process can affect a potential nominee came in 1987 during Judge Robert Bork's failed nomination to the high court. The ABA committee was deeply divided, with four members rating him "not qualified." 

That was deemed a very significant factor by then Senate Judiciary Committee Chairman Joe Biden -- who as vice president is heading up the White House search this time around, sources say.  

FOX News' Shannon Bream contributed to this report.