Last week, the deputy attorney general, Rod Rosenstein, named the former FBI director Robert Mueller as special counsel to investigate “any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump”. Mueller may also examine “any matters that arose or may arise directly from the investigation”. He is empowered to “prosecute federal cries arising from the investigation of these matters”.

This is a very big deal, as you surely know if you have recently glanced in the general direction of any newspaper. Defenders of the rule of law had spent months calling for a special counsel. Finally, they got their wish: an special counsel focused on Trump and Russia. Trump responded by fuming and cowering in the White House.

Robert Mueller: who is the Trump-Russia investigation's special counsel? Read more

Mueller’s appointment is a good thing. These extraordinary times call for a special counsel, armed with access to the FBI’s investigatory arsenal. If crimes were committed, they must be punished. And given the extent to which the attorney general and his deputy are tainted by impropriety, only a special counsel could credibly oversee the FBI’s probe.

That said, Mueller is no silver bullet. To the contrary, he is limited in ways that will prevent him from answering important questions in an open, timely, and transparent manner. Accordingly, while some have urged that congressional investigations (and calls for impeachment) take a back seat while Mueller works, that is the wrong conclusion. If anything, the appointment of a special counsel confirms the need for a vigorous, bipartisan congressional review of attacks on America’s political order.

The first limitation on Mueller’s inquiry is timing: it will take him 12 to 18 months, if not longer, to conduct an exhaustive investigation. Throughout that process, he will keep his timeline secret. It is absurd to expect the public to sit on its hands indefinitely – possibly through the 2018 midterm elections – waiting to learn whether the president and his staff will be charged with treason, perjury, espionage, obstruction or other crimes. The nation needs answers, and it needs them sooner than Mueller can deliver.

This leads to a second issue: secrecy. If Mueller concludes that nobody should be charged with a crime, departmental custom dictates that he say little more. And if he does bring charges, he might reveal only the information necessary to prosecute those specific cases. In the end, even if he wanted to do so, it would be exceptionally difficult for Mueller to tell the public what he found and how he made his decisions.

Those decisions, moreover, are of a highly particular character, and that raises a third issue. As Leah Litman emphasizes at the Take Care blog: “The jurisdiction of the special counsel is seemingly limited to investigations of criminal law, and applications of criminal law to whatever the facts may be.” Thus, Mueller is not empowered to indict conduct – including evil, abusive, or immoral acts – unless that conduct is specifically covered by the criminal code.

This is not a free pass: there are powerful arguments that Trump has violated federal obstruction of justice laws. But to twist a cliché, when all you have is a hammer, everything either looks like a nail or falls out of focus. Mueller has been tasked with finding criminal acts. If he instead finds shocking abuses of power that do not amount to crimes, his duty is to keep silent. The public, though, has a right to see the full picture.

Yet another limit on Mueller is that he remains bound by justice department policies. This arguably, though not necessarily, includes internal precedent concluding that the president cannot be indicted while in office. It also includes a degree of oversight by Rosenstein – who, as Dan Hemel recently remarked, has not recused himself despite the “fundamental principle that nemo iudex in causa sua: no man should be the judge (or the prosecutor) in his own case”.

Notably, Rosenstein is empowered to request an explanation from Mueller for any decision – and to overrule that decision if he deems it “inappropriate or unwarranted under established [Justice] Department practices”. (In that event, Rosenstein must provide a written explanation to Congress.) It is also possible, though this is contested, that Trump could either repeal the special counsel regulations or order that Mueller be fired.

Finally, Mueller is vulnerable to attacks by Trump. As Reuters has reported, Trump’s lawyers may use conflict of interest laws to stymie Mueller’s probe into Jared Kushner and Paul Manafort. Yes, you heard right: Trump could use conflict rules against his opponents. While irony has flowed freely since Trump took office, rarely has it been so finely distilled.

In addition, Trump has repeatedly denounced Mueller’s “witch-hunt”. As Bob Bauer observes, Trump has thus begun “laying the foundation for moving against the investigation at some point in the future”. Over time, such pressure might dull Mueller’s resolve, or his boldness.

Americans must therefore admit that the special counsel, though vital, cannot be their savior. The view that Mueller is looking into all this, and so we can return to our regularly scheduled programming, is mistaken. Instead, all eyes must now turn to Congress.

The bottom line is simple: our nation faces unprecedented questions about the president’s entanglement with a hostile foreign power – through his senior staff, his official campaign, his private bank account and his troubling reception of their envoy. These questions relate directly to a cyber-attack on the US electoral system and to Trump’s own assault on the rule of law.

In confronting this threat, the public needs a quick, wide-ranging, and transparent investigation far more than it needs years of secrecy, possibly followed by an indictment. For that reason, it needs a governmental actor entrusted with broad powers – from subpoenas to sanctions to impeachment – to serve as its champion. In short, it needs the legislature.

Unlike a special prosecutor, Congress can check and balance (and remove) the president for reasons that transcend the metes and bounds of criminal law. It can consider, all at once, the panoply of Trump’s abuses, from emoluments to the Comey firing to Russian electoral interference. It can render its own judgments on Trump’s motivations, or can determine that no motives would justify Trump’s acts. And it can mix political and legal considerations in assessing which of its powers is properly deployed to defend the constitution in this brave new world.

Perhaps most important, Congress can investigate openly and continuously, so that whatever conclusion it reaches is based on the latest information and a full airing of the evidence. We need to rid the executive branch of abuse, corruption, cover-ups, and foreign influence – and we need to do so in a way that proves to the public (and the world) that our democracy works.

It may be naïve to hope that this Congress will live up to the task that history demands. But the nature of the constitution is to ask great things of fallible men and women. As Benjamin Franklin remarked, the framers gave us “a republic, if you can keep it”. We will soon learn if the American people and their leaders can rise to the challenge.