(Leahy? One should hope it starts with the anthrax attacks!)
Having only read this one article, and given that Leahy has not advanced the proposal formally, all we have to go on is the suggested title of a "truth and reconciliation commission." This refers to the South African model after apartheid, under the Mandela presidency. If it really followed the SA model, it would be more radical than you seem to think.
(So here's some relevant cut-pasta from elsewhen...)
The Truth and Reconciliation Commission process did not entail simply letting criminals off the hook. The main goal of the TRC was full exposure of the truth, so that future generations would know their own history.
Amnesty from prosecution was provided only in exchange for a complete accounting of everything one knew about what had really happened under the regime. Many who refused to testify were, in fact, prosecuted. As a result, the members of the apartheid regime and the former SA police and military testified at length about their horrific crimes, describing many cases of murder, torture, subversion and conspiracy, preserving the historical record.
Also, in the process, they got away with their crimes as individuals.
But South Africa under Mandela chose this route so as to
a) avoid a meltdown of South African society due to sabotage by reactionary elements and total white flight (with attendant loss of capital);
b) actually get the full, true history of what happened under apartheid (which would not have been the case otherwise) and prevent the rise of revisionist mythologies;
c) achieve a genuine if limited reconciliation, bringing many whites in as allies to the new order rather than as enemies.
Measured against the common expectations of what post-apartheid South Africa would be like -- that it would face white sabotage or lose all the whites, descend into civil war, and turn into a complete hunger state like present-day Zimbabwe -- it may indeed be the case that the TRC solution was the best possible compromise.
Emphasis on the "possible."
As for the crimes of the United States government, including the Bush regime and the deep state entities with their far-ranging international crimes against many nations stretching out over decades: Of course I would prefer a kind of global Nuremberg process that didn't compromise by offering amnesty in exchange for truth, and put all of the top-level bastards away for the rest of their lives.
So what does Obama appear ready to offer in the real word? It's looking like a repeat of the utterly disastrous Clinton-era "move on" formula, which exposed nothing and left the first set of Bush regime criminals completely free to go on to new pastures and profitable careers, and ultimately to return to power and commit even greater crimes.
Compared to that, the truth and reconciliation process as it was practiced in South Africa was certainly a world better. To take one example, I think it would be better to get a full confession from the liars like Feith et al. about how they engineered the justifying propaganda for the Iraq invasion, although they knew that there were no WMDs (as everyone knew, you can be certain). If this meant that those who lied the country into war and killed a million innocents got amnesty, it would be incredibly fucked up.
At least it would at least end their careers as political operators, and it would be better than what we are likely to get: No confession. No history. The full truth remains classified. We are treated to corrosive revisionist mythologies that encourage reaction and fascism. The perpetrators remain completely free to plot their next crime, their next usurpation.
Again, I think Nuremberg is the better model.
But assuming it's the only alternative to a "Clinton solution," do I support a TRC process for the United States? I'm all for it as a possibility. It might be more radical than a few isolated prosecutions of the worst perpetrators. It would probably lead to some prosecutions of those who refused to participate. More importantly, it would mean throwing open the entire record of American government crime. It would mean a huge, all-consuming purging of the country and its hidden history.
(Anyway, this probably isn't what Leahy's aiming for! I know!)