An ugly episode nearly nine years ago involving a reprimand against Colorado Republican Senate candidate Ken Buck, while he was serving at the time as an assistant U.S. attorney in Denver, continues to shadow the candidate — as well it should.

When an assistant federal prosecutor is reprimanded by the Department of Justice for improperly disclosing internal government deliberations about a pending case to a defense attorney, it is not something that can or should be sloughed off as a youthful indiscretion.

Buck’s opponent in the GOP primary, Jane Norton, had raised the issue of Buck’s 2001 reprimand during this summer’s primary battle, but its importance was largely lost in the heat of that contest. Moreover, because the incident involved an investigation of improper firearms sales by a then-licensed gun dealer in Aurora, the important ethical aspect of the matter was obscured by the emotionalism that almost invariably attaches itself to Second Amendment issues. This is unfortunate, because the episode raises legitimate concerns about ethics, professionalism and loyalty in one of the most sensitive of public jobs — that of a federal prosecutor.

The basic facts of the case appear largely undisputed. In 1998, an investigation was presented to Buck, serving at the time as one of the top assistants in then-U.S. Attorney Henry Solano’s office. The investigating agency, Alcohol, Tobacco and Firearms, believed a firearms dealer in Aurora was engaged in the sale of guns to so-called “straw buyers,” in violation of federal law. Buck declined to pursue the prosecution, and the ATF apparently did not at the time appeal that decision to Solano.

Shortly thereafter, Tom Strickland, Solano’s successor, decided to review the gun case — as was his prerogative as a U.S. attorney. He elected to present the case to a grand jury, which returned an indictment against Greg and Leonid Golyansky and Dmitriy Baravik. And that’s when the trouble began.

There obviously was disagreement within the U.S. attorney’s office over the decision to pursue the case against the alleged firearms violators, something not unheard of. Normally, such internal opinions are kept within the four walls of the prosecutor’s office. This is not only ethical and professional, but pragmatic as well. If word were to leak out — especially to a defense attorney — that questions about the strength or weaknesses of the government’s case had been raised internally, this would almost certainly provide grist for defense arguments to the judge and the jury; and would at least indirectly pressure the government to settle the case more favorably to the defendant.

Yet this is exactly what Buck did. He revealed to a defense attorney the fact that there was an internal government memorandum outlining possible weaknesses in the government’s case. Buck did this, even though by his own admission he had not seen the internal memo. Not surprisingly, two years later the case was finally concluded against the three defendants on terms far less favorable to the government than it likely could have obtained had the defense not been tipped off by Buck.

Buck’s clearly improper communication to a defense attorney about a pending prosecution was not only contrary to ethical and professional standards that govern attorneys; it also represented an act of disloyalty toward his superior — U.S. Attorney Strickland.

Strickland sent the matter of Buck’s improper communication to the appropriate Justice Department office in Washington, and a formal letter of reprimand was issued in December 2001. Buck resigned shortly thereafter.

It is important to note that the U.S. attorney who gave Buck the reprimand was a Republican, John Suthers. This was not a partisan effort to “get” Ken Buck. Nor are the questions the incident raises those of an everyday, “off-the-record chat” between a prosecutor and a defense attorney, as Buck now characterizes the incident. To continue to belittle this incident serves only to reinforce the concerns that were the basis of the 2001 letter of reprimand in the first place.

Republican Bob Barr served as U.S. attorney in Atlanta from 1986 to 1990, as a member of the U.S. House of Representatives from 1995 to 2003, and is now on the NRA’s board of directors.