In these days of legislative gridlock, there is a tendency to look back at the good old days when lawmakers all got along because they shared a whiskey at the end of the workday and socialized on D.C. weekends rather than returning home.

Such social interactions, we are so often told, lubricate the legislative process and round off the rough edges of partisanship.

There is much truth in this, however heavy hangs the air of dreamy nostalgia over this wonderland of bipartisanship.

But there is also a deeper, less noticed — or at least less reported — aspect to the myth of congressional bonhomie, and Georgia College & State University history professor Rachel A. Shelden vividly reveals it in “Washington Brotherhood: Politics, Social Life, and the Coming of the Civil War.”

Simply put, all that bonhomie didn’t keep the country from falling apart. Shelden makes a compelling case that it left Washington ill-prepared for the demise of the union.

The period she covers runs from the late 1840s through the beginning of the Civil War. Then, as now, Capitol Hill was a community unto itself. Unlike today, however, lawmakers were pretty much trapped in Washington for the duration of the session. No jets whisked them home for long weekends.

So the capital became their home, “a tight-knit Washington community that included a vibrant social and cultural life in the mid-nineteenth century,” in Shelden’s description.

Living in close quarters with the opposition presented some challenges, but for the most part, these men (and their wives) saw themselves as the same polity — “a Northerner may have opposed slavery,” Shelden writes, “but he was also a drinking buddy or an expert card player. To a large degree, then, these men came to see each other as part of a fraternity of Washington politicians.”

To flourish in this kind of environment, it was necessary to separate the personal from the political.

Tirades from the floor are a prime example.

Shelden does an admirable job in illustrating how what is said on the floor of the House or Senate might not always be the best guide for historians (or reporters) to figure out what is really going on. Much of the most extreme rhetoric, termed “buncombe,” was intended for consumption back home. The in-crowd knew to ignore it.

But Shelden goes a bit too far in dismissing the efficacy of official debate, and her subjects might have made the same mistake.

When Georgia Whig Robert Toombs took to the floor in December 1849 to savage the Wilmot Proviso — a proposal to ban slavery in territory acquired in the Mexican War — some congressional insiders dismissed it as a stunt, intended only to mollify the constituents back home. Toombs was known as a compromise man, not a fire eater.

But if any issue in 19th-century politics can serve as a warning about the implications of ignoring message-sending, it should be the Wilmot Proviso. The proviso itself was considered by many to be a stunt. That stunt evolved into the single greatest emblem of sectional divide in the decade leading up to the Civil War.

The hundreds of men who died at Burnside’s Bridge as Toombs’ outmanned brigades poured fire down on them from the bluffs above Antietam Creek almost 13 years after his Wilmot Proviso speech might have given the Georgian’s 1849 threats of disunion a more serious hearing than his contemporaries (or Shelden), had they been in attendance.

It’s fine to guard against an over-reliance on the official record. But, as it turned out, the perceptions created by all that thunder and theater proved to be a more reliable indicator of the mood of the country than did the pleasant social interaction of the insulated Washington set, as Shelden herself ably demonstrates.

Washington society in the 1840s and 1850s was a highly organized and ritualistic affair. Lawmakers and other government officials would make calls, host parties, dance at balls and attend levees without regard to political differences.

Housing patterns reflected the nonpartisan nature of the capital, with Democrats and Whigs, Northerners and Southerners sharing rooming houses and hotels.

All this social interaction helped grease the legislative wheels, despite the often hostile nature of debate in Congress.

Viewed through the lens of history, the 1856 caning of Massachusetts Sen. Charles Sumner by Rep. Preston Brooks of South Carolina is seen as a turning point in antebellum America. At the time, “the overwhelming response of Washington politicians was to move on from the event,” Shelden writes. The attack happened in May. By June, the “Sumner affair” had “flamed out.” Even Sumner noted after the attack that “Republicans fraternize most amiably with men who sustain every enormity, even with those who were accomplices after if not before the act under which I am suffering.”

All this fraternizing served a useful purpose. It made legislating possible even in the face of irreconcilable differences over slavery.

Hardly anyone was immune.

Abraham Lincoln, during his one term in the House, was part of a clique that called itself the Young Indians, which included Toombs and future Confederate Vice President Alexander Stephens. Lincoln backed slaveholding Mexican War hero Zachary Taylor for president in 1848, even though he had opposed the war. Taylor, he thought, would help the Whigs carry Illinois.

Among the most accommodating lawmakers was William Seward, considered a radical by many. One of his closest friends was Jefferson Davis.

But while the insularity of the congressional community aided the legislative process, it had dire consequences for the union.

Betrayed by their own friendships with each other, many lawmakers failed to see the ferocity of the coming storm. In 1860, Stephens remembered Lincoln as “just as good, safe and sound a man as Mr. Buchanan” and was certain he “would administer the Government so far as he is individually concerned just as safely for the South and as honestly and faithfully in every particular.”

Lincoln was no radical, but no one who had been paying close attention through the 1850s could seriously believe he would offer no change in policy from President James Buchanan. Stephens was blinded by his personal relationship.

Lincoln had much the same kinds of delusions, wildly underestimating Southern intransigence. And why not? All the men he knew from the South were calm, reasonable men with whom one could share a drink, a game of whist and a good story.

When it all came crashing down, they could hardly believe it.

The current nostalgia — or fauxstalgia, a nostalgia for things one never personally experienced or that never really happened — for the halcyon days of Tip and the Gipper or Dirksen and LBJ cutting deals, ignores two salient realities.

One is obvious, if too often ignored: Those days weren’t nearly as halcyon as today’s dreamers would have us believe.

The other reality is that the parts that were halcyon — the legislative horse trading and back scratching — led to $17 trillion in debt, with no end to the red ink in sight. Yes, they got along. All too well.

Like Abraham Lincoln and Alexander Stephens, William Seward and Jefferson Davis, many modern politicians and pundits prize cooperation above confrontation. But all that antebellum cooperation sowed the wind and, eventually, reaped the whirlwind.

That’s the thing about irrepressible conflicts, to use Seward’s most famous phrase. They’re hard to repress, even with the best intentions.

John Bicknell is a former editor at CQ Roll Call and author of the forthcoming “America 1844: Religious Fervor, Westward Expansion and the Election That Transformed the Nation,” to be published in fall 2014 by Chicago Review Press.