That limitation is in place because Horowitz doesn’t have any jurisdiction outside the DoJ. Horowitz was careful to emphasize that in his official statement:

The DOJ Office of the Inspector General (OIG) is initiating an investigation into whether any former or current DOJ official engaged in an improper attempt to have DOJ seek to alter the outcome of the 2020 Presidential Election. The investigation will encompass all relevant allegations that may arise that are within the scope of the OIG’s jurisdiction. The OIG has jurisdiction to investigate allegations concerning the conduct of former and current DOJ employees. The OIG’s jurisdiction does not extend to allegations against other government officials.

The OIG is making this statement, consistent with DOJ policy, to reassure the public that an appropriate agency is investigating the allegations. Consistent with OIG policy, we will not comment further on the investigation until it is completed. When our investigation is concluded, we will proceed with our usual process for releasing our findings publicly in accordance with relevant laws, and DOJ and OIG policies.

Horowitz will investigate those within his jurisdiction, ie, current and former DoJ officials and employees. He won’t investigate others, but his findings could certainly form the basis for further law-enforcement action. That might also include a number of non-DoJ personnel, up to and including Donald Trump.

If you have not yet read Allahpundit’s post from Saturday, this is a good time to get up to speed on the allegations. In brief, the NYT’s sources — anonymous for now — alleged that acting Civil Division chief Jeffrey Clark pitched Trump on a plan to remove acting Attorney General Jeffrey Rosen, who was not playing along on Trump’s attempts to call the election results into question. The plan as outlined by the NYT’s sources was to force Rosen out, put Clarke in his place, and then use the DoJ to pressure states (Georgia to start, and then move on) into withdrawing their certifications on election results by claiming they had evidence of fraud. Only the threat of a mass walk-out at the DoJ put an end to the scheme, according to the NYT.

Clark, it should be noted, denies the whole thing ever took place. He also has some indirect circumstantial evidence in his favor:

Mr. Clark categorically denied that he devised any plan to oust Mr. Rosen, or to formulate recommendations for action based on factual inaccuracies gleaned from the internet. “My practice is to rely on sworn testimony to assess disputed factual claims,” Mr. Clark said. “There was a candid discussion of options and pros and cons with the president. It is unfortunate that those who were part of a privileged legal conversation would comment in public about such internal deliberations, while also distorting any discussions.”

Mr. Clark also noted that he was the lead signatory on a Justice Department request last month asking a federal judge to reject a lawsuit that sought to pressure Vice President Mike Pence to overturn the results of the election.

That’s hardly conclusive, but it does call into question the narrative that Clark wanted to abuse the DoJ’s authority to overturn the election. Perhaps Clark just favored one method over the other in the election-overturning project. On the other hand, it might also be that the NYT’s sources made a mountain out of a molehill of a legal conversation, perhaps amplified by people unhappy with the final meltdowns within the Trump administration and especially over the sacking of the Capitol on January 6th.

One would be an egregious attack on the rule of law and the electoral institutions of the nation. The other would be an egregious example of media bias and hyperbole. The good news here is that Horowitz might be the only person with enough credibility across the political aisle to unlock this mystery. Practically everyone else has too much of an axe to grind either way to produce a conclusion about what Clark, Trump, and others may or may not have been trying in the final days of the administration.

This might be good news for Trump … but only if he has nothing to hide, and it won’t matter in the meantime. Horowitz could end up clearing him, but it will likely take months rather than hours for an IG probe to reach any firm conclusions. It might have the effect of keeping the Senate from delving into this at an impeachment trial for two reasons. One, Congress usually avoids interfering with active investigations at the DoJ, and two, the article of impeachment doesn’t relate to this allegation anyway. To make this relevant in the trial, the House would need to impeach all over again, which they might … but now would likely wait for Horowitz to either confirm it or debunk it. Impeaching on this only to have Horowitz later say it never happened would be a very large political problem for House Democrats.

If Trump and Clark really did do what the NYT reported, then Horowitz’ probe is very bad news. It might be bad news for the Biden administration as well, however. Horowitz would have plenty of people to interview/interrogate as to the particulars, and if officials conspired to subvert an election, Horowitz would likely make criminal referrals to the DoJ. That might not be the most welcome news for incoming AG Merrick Garland or Joe Biden himself, who would likely prefer to stay away from prosecutions if they can help it. Horowitz might prove himself to be a uniquely bipartisan fly in the ointment.