FBI agents look for evidence at Eugene Simpson Stadium Park in Alexandria on June 15. A gunman shot Rep. Steve Scalise (R-La.) and four others at the park on June 14. (Bonnie Jo Mount/Washington Post)

Norman J. Ornstein is a resident scholar at the American Enterprise Institute.

The horrific shooting last week on a group of Republican lawmakers playing baseball left House Majority Whip Steve Scalise in critical condition and hospitalized others — including two brave Capitol Police officers. The outcome is tragic, but it could have been much worse. Had the gunman been successful in killing members of Congress, we would have had an immense crisis of governance for our constitutional system.

The only reason those two officers were at the baseball field with a contingent of Republican lawmakers was the presence of Scalise, who has a security detail as a congressional leader. Without them, the gunman would have had an unimpeded opportunity to shoot at the helpless crowd of representatives, senators, aides and bystanders for many minutes before local police arrived. He could have killed two dozen lawmakers, among many others.

Such a disaster could have threatened the Republican majority in the House for an extended period, because the only way to fill a vacancy in the chamber is by special election — and those elections take months. With a series of critical decisions looming, including keeping the government funded, raising the debt ceiling and more — not to mention the investigations into the involvement of the president and his key aides and staff in Russian interference in our election and possible obstruction of justice — the nature and legitimacy of those decisions would be clouded.

(Monica Akhtar,Jenny Starrs,Lee Powell,McKenna Ewen,Bastien Inzaurralde/The Washington Post)

Here is the most likely scenario: Paul D. Ryan would have remained speaker of the House and controlled the agenda, but anything he introduced would have been defeated on the floor or altered to fit Democratic priorities. In any event, little produced by the House would have passed the Senate. Meanwhile, the majority would have shifted to Democrats in many committees, making the likelihood of any action during this time slim.

For those left of center, such a failure of government in the face of a Trump-Pence-Ryan agenda might be fine, but it would not meet any test of legitimacy. Plus, imagine 30 special elections at a time of broader political turmoil. Maybe Democrats win enough seats to take the majority or deadlock the House. Such a victory would be highly problematic and certainly not anything the Framers contemplated.

This should be a wake-up call for Congress to act and ensure the continuity of our constitutional framework. Our government’s vulnerabilities have been starkly evident since the attacks on Sept. 11, 2001. We know that Flight 93 headed for the Capitol dome, and that it was only thwarted thanks to the actions of its brave passengers. Had the plane hit the Capitol, it could have killed or disabled more than half of Congress. The Constitution flatly requires a quorum of a majority of its membership to do any official business, so at the worst possible time, the system could have been beheaded. No Congress for months would have meant martial law or its equivalent.

I noticed this dilemma on the afternoon of 9/11 and began to write about it within days. Shortly thereafter, I joined with my colleagues Tom Mann and John Fortier, along with former White House counsel Lloyd Cutler and former senator Alan Simpson, to create a Continuity of Government Commission. After extensive deliberations, we issued three reports on the gaps in continuity for the Congress, the president and the Supreme Court.

For Congress, we need a constitutional amendment that gives emergency powers to governors to fill vacancies with interim appointments until special elections are held and that accounts for the incapacitated and missing until they can resume their duties. For the presidency, we need to rewrite the 1947 Presidential Succession Act so that qualified individuals outside the capital can step in following a massive attack. For the Supreme Court, which only has a statutory quorum requiring six justices to function, we need to create an Emergency Interim Court of Appeals, consisting of remaining justices and the chief judges of the 13 circuit courts.

The response by Congress to these recommendations? Next to nothing. Republicans under speaker Dennis Hastert refused to act, but so did Democrats after they recaptured the majority. The proposals stalled due to a combination of inertia, ardent opposition to appointments in the House and superstition (the same phenomenon that makes people think writing a will makes them more vulnerable).

Our vulnerability to terrorism remains great; we know that decapitating our government is a prime goal of terrorist organizations. But the Alexandria shootings tell us that even a single, deranged lone wolf with easy access to rifles and high-capacity magazines can wreak havoc on our government. This incident is our second major wake-up call. Will Congress finally do its duty to the country and the Constitution?