House Republican investigators warned their Democratic counterparts to “stop trying to derail the [IRS] investigation,” in light of the Treasury Department inspector general’s letter to Democratic leaders explaining that liberal groups were not subjected to the same scrutiny that Tea Party groups experienced.

“Our Democratic colleagues should stop trying to derail the investigation by defending IRS officials with distorted claims equating the systematic scrutiny of Tea Party groups with the more routine screening progressive groups received,” said House Oversight and Government Reform Committee Chairman Darrell lssa, R-Calif., in a statement today. “As TIGTA notes, Tea Party groups and progressive groups were treated very differently by the IRS.”

House Democrats released documents this week suggesting that IRS officials were asked to “be on the lookout” for progressive groups as well as Tea Party groups, which provided the basis for Democrats to argue that the IRS did not target conservatives based on ideology. They also scolded the Treasury Department inspector general, J. Russell George, for reporting that the IRS had targeted conservatives.

“The audit served as the basis and impetus for a wide range of congressional investigations and this new information shows that the foundation of those investigations is flawed in a fundamental way,” Rep. Sander Levin, D-Mich., the top Democrat on the Ways and Means Committee, wrote to the inspector general.

The inspector general replied today, explaining that the IRS disproportionately targeted Tea Party groups — 292 conservative groups, compared to just six liberal groups.

“In total, 30 percent of the organizations we identified with the words ‘progress’ or ‘progressive’ in their names were processed as potential political cases,” George wrote Levin. “In comparison, our audit found that 100 percent of the tax-exempt applications with Tea Party, Patriots, or 9/12 in their names were processed as potential political cases during the timeframe of our audit.”

And the liberal groups were not scrutinized based on their ideological leanings, unlike the Tea Party. George explained that “while we have multiple sources of information corroborating the use of Tea Party and other related criteria we described in our report, including employee interviews, e-mails, and other documents, we found no indication in any of these other materials that ‘Progressives’ was a term used to refer cases for scrutiny for political campaign intervention.”

“Both the Ways and Means and Oversight Committees are methodically working through an investigation following up on the IG audit,” Issa said in his statement today. “Ranking Member Cummings and Ranking Member Levin need to join us in this investigation and not look for every excuse to just say the case is solved and Congress should move on.”