For more than 200 years, the reins of America's leadership have been peacefully handed over from one administration to another, regardless of party affiliation, in part because we have never seriously indulged in criminalizing our political differences.

My Russian immigrant father, who fled Communist persecution, told me more than once that avoiding political persecutions and show trials was crucial to preserving our republican form of government. But Sen. Patrick Leahy (D-Vt.) and House Speaker Nancy Pelosi (D-Calif.) are now proposing something that may well result in criminalizing policy differences.

Leahy has scheduled a hearing Wednesday on his proposal to convene a "truth commission" to conduct inquiries into Bush administration decisions on terrorist detainees, interrogation procedures and other practices. As precedent, Leahy cited the Truth and Reconciliation Commission, which was convened in South Africa to investigate the barbarous practice of apartheid.

That outrageous comparison falls flat. For one thing, Leahy's "truth commission" is not needed to serve any legitimate government function. Effective government oversight has never required such commissions. Moreover, Sen. Carl Levin (D-Mich.) held hearings, under oath, over a 2½- year period looking into many of the same issues. His report, though predictably partisan, found no criminal violations.

Why, then, does Congress need a truth commission at this point in time? Only because the findings of previous investigations didn't suit the far left's tastes?

Nevertheless, those pushing for a truth commission have made it very clear that they have already determined the guilt of the Bush administration. The proposal, therefore, seems targeted to define political crimes in the spirit of, "We won, which means that the former regime is criminal."

There is no other purpose to such a commission. If crimes were really committed, federal prosecutors can investigate and prosecute. If new legislation is required, Congress should implement it through the normal legislative process. The same is true if Congress wants to reorganize its intelligence committees or internal reporting structures. The commission cannot be used for impeachment purposes, so there is no real constitutional or legal reason for an "independent" commission.

The proposed truth commission thus more closely resembles the Moscow trials staged by Joseph Stalin in the 1930s than the legitimate inquiries in South Africa. Stalin's show trials provided a showcase for inflammatory claims and predetermined judgments. They were a ruthless, cynical and chillingly effective means of purging inconvenient opponents and critics. Sound familiar?

Congress should be very reluctant to approve Leahy's proposal. After all, in these so-called crimes, members of Congress participated as conspirators when it repeatedly funded the Bush programs. Before Congress creates any commission, it should expose its own failures, if indeed there were any, to stop these practices.

Many of the same members who are so critical today remained silent when they were briefed about our counterterrorism efforts. In December 2007, The Washington Post reported that in 2002 four members of Congress were given a virtual tour of the CIA's overseas detention sites and were briefed on interrogation techniques. The bipartisan group, which included Pelosi, was specifically briefed on waterboarding. None of the four complained, and one of them asked if the methods being used were tough enough.

The CIA gave key legislative overseers about 30 private briefings, including waterboarding and other interrogation techniques in 2002 and 2003. It is curious that lawmakers who were repeatedly briefed and raised no objections should subsequently criticize those very same policies. That the criticism came only when memories of the Sept. 11 attacks faded and public opinion shifted suggests a political motive. If that is the case, trying to prosecute those involved is the concomitant attempt to criminalize these political differences.

Advocates of the commission should have a second concern, too: It will only harden partisan battle lines and ensure that public discourse becomes increasingly strident.

The Internet is filled with postings whose tenor is: "If you are on the other side of the political fence and hold different views on how to address our nation's problems, you must be evil, corrupt and, yes, a criminal." This commission will only exacerbate that problem.

Third, if the Obama administration and congressional leaders start deploying McCarthyite tactics against their former political opponents, they risk losing public support for their efforts to resolve our economic problems.

Finally, President Barack Obama should be especially wary of efforts to criminalize policy decisions of prior administrations; one day his staff will join the ranks of former administrations. The realities of governing already have led Obama to continue "controversial" positions on detaining enemy combatants and asserting the state secrets privilege. Does he really want to see honest differences of opinion on such questions -- many of which do not enjoy support in his own party -- become criminal issues?

Obviously, Leahy and Pelosi view national security and public policy differently than did the Bush administration. They disagreed on the solutions to many of the problems faced over the past eight years, including how to fight a war against terrorists. But differences of opinion are not criminal. Exposing the prior administration to prosecution for these differences will impose great hardship on many individuals and create a precedent to criminalize public service in the future.

Moreover, it will impair the ability of government officials to deal with serious and ongoing problems. If Leahy is successful, his "truth commission" will do untold damage to the fabric of our political system.

Hans A. von Spakovsky is a visiting legal scholar at the Heritage Foundation. He is also a former commissioner on the Federal Election Commission and counsel to the assistant attorney general for civil rights at the Department of Justice.