The University of Cornell School of Law sees it a bit differently:

No provision of the Constitution expressly authorizes either House of Congress to make investigations and exact testimony to the end that it may exercise its legislative functions effectively and advisedly. But such a power had been frequently exercised by the British Parliament and by the Assemblies of the American Colonies prior to the adoption of the Constitution.161 It was asserted by the House of Representatives as early as 1792 when it appointed a committee to investigate the defeat of General St. Clair and his army by the Indians in the Northwest and empowered it to “call for such persons, papers, and records, as may be necessary to assist their inquiries.”162

The Court has long since accorded its agreement with Congress that the investigatory power is so essential to the legislative function as to be implied from the general vesting of legislative power in Congress. “We are of the opinion,” wrote Justice Van Devanter, for a unanimous Court, “that the power of inquiry—with process to enforce it—is an essential and appropriate auxiliary to the legislative function. . . . A legislative body cannot legislate wisely or effectively in the absence of information respecting the conditions which the legislation is intended to affect or change; and where the legislative body does not itself possess the requisite information— which not infrequently is true—recourse must be had to others who possess it. Experience has taught that mere requests for such information often are unavailing, and also that information which is volunteered is not always accurate or complete; so some means of compulsion are essential to obtain what is needed. All this was true before and when the Constitution was framed and adopted. In that period the power of inquiry—with enforcing process—was regarded and employed as a necessary and appropriate attribute of the power to legislate— indeed, was treated as inhering in it. Thus there is ample warrant for thinking, as we do, that the constitutional provisions which commit the legislative function to the two houses are intended to include this attribute to the end that the function may be effectively exercised.”163

And in a 1957 opinion generally hostile to the exercise of the investigatory power in the post–War years, Chief Justice Warren[p.91]did not question the basic power. “The power of the Congress to conduct investigations is inherent in the legislative process. That power is broad. It encompasses inquiries concerning the administration of existing laws as well as proposed or possibly needed statutes. It includes surveys of defects in our social, economic or political system for the purpose of enabling the Congress to remedy them. It comprehends probes into departments of the Federal Government to expose corruption, inefficiency or waste.”164[Emphasis mine.]

Justice Harlan summarized the matter in 1959. “The power of inquiry has been employed by Congress throughout our history, over the whole range of the national interests concerning which Congress might legislate or decide upon due investigation not to legislate; it has similarly been utilized in determining what to appropriate from the national purse, or whether to appropriate. The scope of the power of inquiry, in short, is as penetrating and far– reaching as the potential power to enact and appropriate under the Constitution.”165

http://www.law.cornell.edu/anncon/html/art1frag9_user.html

So yes, Congress can investigate and that investigation is not limited to doing so solely for the purposes of legislation.

You and Olbermann are both displaying a shocking lack of awareness. The legislature is preparing to investigate. There is plenty of reason to invoke a special prosecutor. There is plenty of judicial room for justice to be served.

By laying all of this outrage at the executive is empowering the unitary executive philosophy by making Obama the prime arbiter of justice. The reason: ignorance of political process. Blaming Obama would make sense if he were a dictator; he's not. Put your energy towards persuading the legislature to do what's right.

I am getting sick of this ignorant misdirected holier than thou smug ridiculous outrage merchandising that is damaging reasonable discourse.

via Wiki:

"In 2002, during a brief visit to the UK, a petition for Kissinger's arrest was filed in the High Court in London based on Indochinese civilian casualties and environmental damage resulting from U.S. bombing campaigns in North Vietnam and Cambodia in the period between 1969 and 1975.[34]

Kissinger, the war criminal, walks the streets of New York freely.

The bombing of Hanoi on December 24, 1972 resulted in harsh reactions from the prime-minister of Sweden, Olof Palme. During his famous speech that same day to the media (nowadays referred to as "The Christmas Speech"), Palme expressed harsh criticism for the war, comparing it with several of Nazi Germany's and Soviet's worst deeds.[18] This froze the diplomatic climate between the United States and Sweden, a freeze that lasted until March 1974.

Lt. William Calley, tried and convicted, My Lai massacre. That effectively puts Lynndie England and Chuck Graner on par with Calley.

Robert S. McNamara? For all of the bluster of the left after Vietnam, nothing.

So let's get real. We tend to like the breastbeating, but don't do anything of consequence.