In 2007, Hans Bader, Counsel for Special Projects of the conservative Competitive Enterprise Institute ranked Blumenthal as "the nation's worst state attorney general", based on "a set of explicit criteria — such as encroachment on the powers of other branches of government, meddling in the affairs of other states or federal agencies, encouragement of judicial activism and frivolous lawsuits, favoritism towards campaign contributors, ethical breaches, and failure to provide representation to state agencies or to provide legal advice." Bader singled out Blumenthal for his role in the tobacco settlement and efforts to regulate carbon dioxide. The report, apparently the work of Bader alone, did not contain a description of the methodology used. All of the ten attorneys general ranked by Bader are Democrats.
In a landmark Connecticut Supreme Court decision, Blumenthal v. Barnes a unanimous court determined that Blumenthal sued the owner of a charter school while lacking authority to bring the suit. Justice Peter T. Zarella concluded in this 2002 opinion that the office of the attorney general is "a creature of statute that is governed by statute and, thus, has no common-law authority."