At the Capitol, this Sept. 11 heralded more than the 15th anniversary of the worst terrorist strike on American soil. It also revived memories of one of the most intense surges of big-ticket policymaking in modern times.

Congress was so infused with a sense of national resolve — mixed with more than a small amount of abject fear — it operated with a measure of apolitical collaboration that’s barely imaginable in the paralytic partisan atmosphere of today.

The aftershock of the attacks kept the cooperative spirit aloft for less than three months, hardly a sustained period of activity on par with the New Deal or Great Society. But the window of legislative opportunity was open wide enough for Republicans and Democrats to move through with equivalent forcefulness, before their political reflexes took over and lawmakers began regretting bits of their boldness.

Some of that buyer’s remorse has only grown in the past decade, especially about the breadth of the authorizations of both military might and governmental muscularity in waging an open-ended war on terrorism. But, in the main, the fall of 2001 provides a heartening reminder that even the most sharply divided Congress can coalesce quickly to produce historic accomplishments — at least if the emergency is profound enough.

An inauspicious start

The year didn’t begin auspiciously in that regard. The 2000 election had produced a Republican capital, but only by a hair: George W. Bush’s contested victory was paired with 50 senators from each party and a 51 percent GOP majority in the House. And then, in early summer, a party switch by Sen. Jim Jeffords of Vermont meant Senate control for the Democrats and the return of divided government. Congress prepared for a fall of budgetary stalemate and positioning for the next campaign.

All that got set aside soon after members began their first full week of work following the August recess.

Tuesday, Sept. 11, began with a chaotic evacuation of the congressional complex, dark smoke visible over the Pentagon as dozens of hearings and markups were abandoned. (The widespread assumption in the Hill community, which has never been established, is that United Airlines Flight 93 was being steered by its al-Qaida hijackers toward the Capitol Dome before auguring into Pennsylvania farmland.)

Rank-and-file members mingled with running crowds in streets snarled with traffic, while the congressional leadership was airlifted to a military bunker in the Virginia wilderness.

But by nightfall, the leaders had returned to join about 200 senators and House members for a brief, and heavily guarded, show of solidarity on the Capitol’s East steps that famously included a spontaneous chorus of “God Bless America.”

The symbolism started evolving toward substance the next morning, and by Friday evening a pair of far-reaching measures had cleared with near unanimity — and, as importantly, after the congressional voices of skepticism and dissent were not only listened to, but also mollified.

Power of the purse

One bill provided $40 billion to recover from the attacks and begin combating those responsible — an extraordinary sum amounting to 6 percent of regular discretionary spending for the year. No lawmaker voted against the extra money, but that belied a significant amount of behind-the-scenes friction that almost derailed the package until hours before the balloting.

When the Bush administration pressed for a blank check, without limits or conditions, Republican and Democratic appropriators alike made clear that, war footing or not, the power of the purse still resided with them. The final deal was a middle ground: Bush got to spend half however he wanted, but the other half was subject to the usual appropriations process.

The lopsided majorities for the second bill, authorizing military force, also masked a fervent and intense debate. Most Republicans were inclined to back Bush, who initially wanted permission not only to punish the attackers but also to use any means necessary “to deter and pre-empt any future acts of terrorism of aggression against the United States.”

But they eventually yielded to most Democrats, who found that proposal way too open-ended and insisted that war be waged only against those with some connection to 9/11. (In hindsight, many on the Hill regret that the measure was not crafted more tightly so it could not, for example, be used to justify U.S. military missions against ISIS.)

Similarly intense deliberations — albeit highly accelerated and relatively free of political melodramas played out in public — were behind the other marquee legislative responses to the attacks enacted by early November.

A $15 billion aid package for the airlines, hobbled by a national fear of flying, got through because Democrats dropped their demands for aid to workers displaced by the attacks. Back dues of $582 million for the United Nations, a would-be partner in combatting terrorism, were delivered after the U.N.’s conservative critics got a few sweeteners.

Responsibility for airport security got federalized when Republicans set aside anxieties about boosting the rosters of public unions. And the government was granted broad new authority to track, arrest and prosecute suspected terrorists when civil libertarians of both parties dropped their objections to all but one of Bush’s major proposals.

Only after Thanksgiving, when the two sides deadlocked over proposals to stimulate the economy away from any post-9/11 downturn, did partisan posturing begin to return as the Capitol’s default setting. Domestic policy and looming electoral considerations were already proving too much for the center to hold.

But for 10 fascinating weeks, faith in the functionality of Congress had been both tested and restored.