An intriguing piece at MarketWatch asks that question and provides substantial evidence that the answer is yes.
Consider these passages:
MCCAIN DIDN'T INVESTIGATE REPUBLICAN COLLEAGUES FOR THEIR ILLEGAL OR UNETHICAL BEHAVIOR
John McCain's Indian Affairs Committee hearings failed to go after federal lawmakers who benefited from Jack Abramoff's lobbying. McCain said his Indian Affairs "committee continues to examine all the financial angles of where the $82 million ended up, as well as other political and charitable contributions the tribes made at Abramoff's request." However, McCain "reiterated that he was following the money trail, not the legislative actions taken by Members of Congress," saying, "We stop when we find out where the money went." [Roll Call, 3/10/05]
MCCAIN ACKNOWLEDGED THAT SOME LEGISLATORS HAD COMMITTED "WRONGDOING", BUT REFUSED TO INVESTIGATE
Asked if he believed that some legislators had committed a crime related the Abramoff scandal, Senator McCain said, "There's strong evidence that there was significant wrongdoing, but I'm not a judge or jury." McCain emphasized though that he would not investigate his colleagues in Congress, declaring: "I will not [investigate members of Congress], because I'm a chairman of the Indian Affairs Committee. This was brought to our--this whole thing started--was brought to us--attention by some disgruntled tribal council members in a small tribe in Louisiana, and we took it as far as we thought was our responsibility, which is where the money ends up." [NBC, Meet the Press, 12/4/05]
And who was one of the biggest beneficiaries of McCain's willingness to look the other way? Why, none other than Alabama Governor Bob Riley.
MCCAIN WITHHELD CONTROVERSIAL EMAIL IMPLICATING AL GOV. BOB RILEY DURING RILEY'S RE-ELECTION CAMPAIGN
As chair of a committee conducting an investigation on Abramoff, McCain had access to an incriminating email involving Alabama Governor Bob Riley. Rather than including the email--which detailed what Abramoff wanted Riley to do in return for the contributions Abramoff's tribal clients directed toward his campaign--in his report on the Abramoff scandal, McCain chose to withhold it, thus shielding Riley from becoming implicated in the scandal as he was waging a bitter re-election campaign. [Huffington Post, 2/25/08]