When the Senate decides this week whether to subpoena documents and witnesses in President Trump’s impeachment trial, it will decide more than just whether former national security adviser John Bolton will give testimony against him — and more even than the future of Trump’s administration. Senators will also be voting on whether to reclaim investigative authority they long ago ceded to the executive branch.

Congress has grown sorely out of practice in conducting its own investigations of presidential misconduct. Since long before Trump, the legislature has become accustomed to waiting for prosecutors to deliver definitive reports rather than doing its own work to gather evidence. The Ukraine case, however, spurred a revival of congressional investigative authority. With no special counsel to turn to, the House of Representatives simply investigated the matter on its own. The question now is whether the Senate will join the House or retreat out of partisan loyalty to the president.

In the early Republic, Congress investigated the executive branch without the involvement of criminal investigators at all. The congressional power to investigate executive branch conduct saw its origins in George Washington’s administration, when a U.S. military force under Gen. Arthur St. Clair was routed by Native American armies in what is now Ohio. The questions were not ones of illegality, but in response to the fiasco, the House took the position that it could serve as the “grand inquest of the nation,” as it was deemed at the Constitutional Convention, and it looked into what had happened. The Washington administration cooperated. Though each branch contested the limits of the other’s authority, this precedent of congressional oversight and executive participation has held ever since.

The idea that the executive branch had a role at all in investigating presidential scandal only began in 1875 with the Whiskey Ring corruption in the Ulysses S. Grant administration. The Whiskey Ring, a network of corrupt distilleries conspiring with federal officials to evade taxes, is the first recognizably modern presidential scandal, complete with a special prosecutor, criminal misconduct in the White House itself, presidential testimony in a criminal proceeding and even the removal of a special counsel for an excess of independence. The Whiskey Ring concluded in several criminal prosecutions, including an unsuccessful one of Grant’s private secretary.

In the 1920s, the Teapot Dome bribery scandal of the Warren Harding administration continued the pattern. Teapot Dome was unearthed by a tenacious congressional investigation, but when the scandal emerged after Harding’s death, the new president, Calvin Coolidge, stepped in to appoint not one, but two special prosecutors to investigate accusations that Harding’s interior secretary had accepted bribes in exchange for oil leases on federal land. A general public expectation still endured, though it was weakened after Teapot Dome, that Congress would take the lead in investigating executive misconduct, and in the next several decades, few presidential scandals tested the proposition.

It was Watergate that profoundly transformed the way Americans understand the investigation of presidential scandal. Watergate famously involved a high-profile congressional investigation — one that riveted the nation and discovered President Richard Nixon’s taping system. But the matter also involved a criminal investigation. Unlike Teapot Dome or the Whiskey Ring, this was an investigation of the president himself, which had never happened before. The Watergate investigation revealed a core problem with the idea of letting the executive branch handle investigations of the president, rather than having Congress take them on: The federal prosecutors who lead such investigations ultimately work for the president, and he can interfere with and even fire them. Watergate thus raised the question of whether a president must tolerate an executive branch investigation that could lead to his own impeachment or criminal prosecution.

The fallout from Watergate has conditioned every subsequent investigation of a president. Watergate led to the passage of the Independent Counsel law, designed to reduce the need for a president to consent to his own investigation. But Watergate also established a public expectation that a presidential scandal would be investigated as a criminal matter, not merely dealt with as a political matter. As such, it shifted the locus of investigation of presidential scandal from Congress to the executive branch. When the Iran-contra scandal came along more than a decade later, the congressional investigation was entirely dominated by that of the prosecutor, independent counsel Lawrence Walsh — which went on for years after the congressional probes ended and uncovered significant evidence that had been withheld from Congress. Indeed, Iran-contra brought the enterprise of congressional investigation into some disrepute when Congress granted limited immunity to two key figures in a manner that resulted in courts overturning their criminal convictions.

To some degree, Congress deferring to executive investigations made sense: The executive branch simply has more powerful investigative tools than does the legislature. But deferring to the executive gave rise to habits of deferring — which is to say habits of Congress not doing its own work.

By Bill Clinton’s impeachment, Congress did not even try. It simply waited on the sidelines for the criminal process to spoon-feed it a factual record. The Clinton scandal broke in January 1998, but Congress did nothing until the Starr Report arrived almost nine months later, and even then, the legislature added virtually no information. Congress effectively treated Starr as its own impeachment investigator. The Whiskey Ring required the president to allow investigation of close associates, and Watergate required the president to tolerate a criminal investigation of himself under threat of impeachment. But by the time of the Clinton scandal, an executive branch officer, acting under the cloak of a criminal investigation, had been converted into an impeachment investigator on behalf of the legislative branch.

The expectations that developed in the wake of Watergate have persisted into the Trump era. The notion that the criminal process is the principal means of investigating presidential misconduct — indeed, the expectation that the legislature will defer to and work from the record established by prosecutors — was plainly visible in the legislative deference to Robert S. Mueller III’s investigation. Both Democrats and Republicans in Congress frequently claimed to be waiting for Mueller’s report before making up their minds, and House investigators took pains to avoid compromising both Mueller’s inquiry and related investigations in the Southern District of New York. It was also visible in the bewildered response to the report Mueller ultimately delivered, which detailed grave wrongdoing but declined to make explicit criminal accusations. Despite what Mueller uncovered, which showed extensive wrongdoing, Democrats were unable to marshal sufficient support to begin serious impeachment proceedings in the absence of a specific finding of presidential criminality.

In the face of this history, it is almost miraculous that when the Ukraine scandal broke last fall, the House dramatically reversed this long-term trend. The Department of Justice quickly made clear it would not investigate the president’s conduct. But Congress, at long last, began to do the work itself, launching a rapidly moving House investigation that produced an extensive factual record and delivering articles of impeachment to the Senate. The House was out of practice, and it struggled to relearn the muscle memory of genuine executive oversight, but it did remarkably well in the face of sustained executive intransigence. The House deposed witnesses, held public hearings and produced a record replete with previously unknown evidence. Congress is capable of effective oversight and investigation when it tries. The Democratic-controlled House has different institutional incentives to expend effort than does the Senate, which is controlled by the president’s party. But the fundamental decision is the same.

The choice before the Senate now is whether to build on the House’s effort and to reclaim the investigative authorities the branch as a whole has long neglected. It is the choice of whether to join in a bicameral resumption of responsibility or to insist on continued abdication.

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