I think the devil is in the details on this one. Do we know, to start with, what the Constitution of the State of IL says on a matter of impeachment? Can impeachment only be done on the basis of a crime, or can other factors be taken into account.Orrologion makes some interesting points. The Illinois State Constitution is closely modeled after the Federal Constitution. With respect to impeachment the matter was deliberately left vague by the framers while setting a high bar (2/3 super majority) for removal by the Senate. When asked about what would be grounds for impeachment the then minority leader of the House of Representatives in the early 1970's Gerald Ford famously responded that "the House could impeach the president for a bad haircut. Getting the Senate to convict is a different story."
As an example, the Clinton impeachment required both a legal proceeding, undertaken by the House of Representatives and presided over by the Chief Justice AND a ratification by the Senate, which required no legal proceedings being a purely political standard. Clinton was (rightly, to my mind) impeached by according to the legal standard and then that impeachment was not approved by the Senate (rightly, again, to my mind, given the fishing expeditions that led to the perjury). The IL Constitution may not require a legal proceeding, or at least not one that demands a specific and overly high bar if the framers intent was to ensure trust between the executive and the legislature (a constitutional ethic of shared weakness akin to Fr. Stephen Freeman's comments on the 'weakness' of Orthodox ecclesiology).
Most constitutional scholars tend to agree that the power of impeachment is not limited to offenses against the criminal code. And it also needs to be noted that this was NOT a criminal trial with criminal sanctions attached. In that sense this was not a "judicial" proceeding.
But it was a process whereby the legislature effectively cast a veto over the last general election in which the people of Illinois elected Blago as their Governor. Also the framers deliberately did not establish a parliamentary system of government here. So I don't think it would be fair to reduce what we saw to the equivalent of a vote of "no confidence" which typically compels a prime minister to resign.
Clearly it falls somewhere between a criminal proceeding and a simple decision by an employer to terminate an employee suspected if inappropriate behavior. I think that while again conceding, this was not a "judicial" proceeding that it was "juridical." Recall that the Senate convened as a “tribunal” for the purpose of “trying” the Governor. It passed a judgment on the Governor that he had abused the powers of his office and in this case committed acts which could be considered criminal and it removed him from office and barred him for life from holding any office of public trust in Illinois.
Further while the process may not have been laid out in any detail, it was a "constitutional" process by which the Governor was removed. A proceeding which is at once both "juridical" and "constitutional" in nature I believe implies the guarantee of at least a modicum of due process rights. One notes that the in the armed forces commanding officers are empowered under the Uniform Code of Military Justice (Title X U. S. Code ) to impose “Non-Judicial Punishment” on servicemen for minor infractions of military discipline such as overstaying leave or mouthing off to a superior. These often informal proceedings are not criminal (they are not Courts Martial) and the punishments are typically limited to reduction in rank, restriction to quarters, assignment of extra duties and fines which normally can not exceed a half months pay per month for two months. But the courts have also consistently held that while such proceedings are not “judicial” they are still “juridical” in nature and that the accused must still be given a fair hearing and an opportunity to offer a defense.
All that said the State Senate is a part of the legislative branch of the government and is co-equal to the other branches including the judiciary. Thus I am not sure that the former Governor has much recourse. The constitution gives the power of removal to the Senate and outside of the 2/3 majority requirement the rest is left to the Senate to determine. Based on this one could make a narrow though compelling argument that the Senate did not violate any of Blagojevich's rights. That's the legal argument.
But my short essay was more about the question of due process as a basic concept of fairness. In that context I think the Senate trial fails miserably. It was not a trial at all. It was a political firing squad thinly disguised as a trial. When one considers that this is the first time Illinois has ever impeached and removed a Governor from office it becomes even more disturbing. For good or ill (I am strongly disposed to believe the latter) this “trial” is now not only a precedent, it is indeed THE precedent. And I think it is a very unfortunate one.