Speaker John A. Boehner’s resignation continues, and possibly cements, a remarkable pattern in modern American politics.

The most powerful position in Congress has also become one of the most unstable jobs in American government. After almost a century of orderly departures and orchestrated transitions, five of the six most recent speakers of the House have now been pushed from the Capitol by circumstances they could not control.

The trend of past three decades will surely make California’s Kevin McCarthy, or whoever ascends to the presiding officer’s chair, extremely wary about his career’s trajectory over the long term — even after this fall’s latest internal Republican revolution gets put to rest.

Assuming this little-noticed rhythm of the House’s political dynamic continues, the 62nd speaker will become one of the nation’s premier nationally polarizing figures sooner rather than later — and not long after that will get sacrificed on the altar of either internal partisan discord or electoral defeat.

This newly inherent job insecurity looks to be as much a product of the multimedia age as of the steady devolving of the legislative branch into near total paralysis.

“As party caucuses become more homogeneous and hence likely more polarized, power shifts from the committee structure to the party leadership,” said Ronald M. Peters Jr. of the University of Oklahoma, who’s written two books about the modern speakership.

“As this has occurred over the past 30 years, House speakers have become subject to partisan attacks,” he added, and not always from the opposing party.

The televising of the House since the 1980s has also fundamentally altered the position, in the view of John J. Pitney Jr., an expert on congressional leadership at Claremont McKenna College. “The extra publicity has made the speakers into major public figures in a way they never were before,” he said. “With that public exposure has come much more risk, both from within Congress and by making them public targets.”

Within those constraints, both professors suggested, Boehner’s days were almost automatically numbered in ways not of his own making.

Or, as he’s said in so many other contexts during a 25-year congressional career distinguished by rising and falling and then rising again in the leadership: “This is not about me.”

In that vein, Boehner had only two pieces of relatively simple advice when asked at his resignation news conference Friday how he’d counsel his successor to be successful at the helm of the House, a post that also comes with the spot second in the line of presidential succession.

“His number one responsibility is to protect the institution. Nobody else around here has an obligation like that,” Boehner said. And other than that, the only viable formula starts with turning a blind eye to both interparty and external partisan pressure and being true to your own vision: “You just do the right thing every day for the right reasons, and the right things will happen.”

On that front, Boehner received an effusive shoutout from President Barack Obama, who characterized his principal counterpart in the legislative battles of the past five years as a “patriot” in part because he “understands that in government, in governance, you don’t always get 100 percent of what you want.”

At his own news conference Friday, the president signaled he’d have little to say come November to a new speaker who would seek to preserve his job by countenancing a government shutdown unless the demands of the confrontational conservatives were met.

The plausibility of such a situation was almost unthinkable when Boehner was a state legislator in Ohio pondering his first run for Congress in 1989. That was the year a speaker resigned in the middle of his term for the first time in more than a century.

In some respects, the reason Democrat Jim Wright of Texas gave up partway through the 101st Congress is the same as why Boehner is handing back the gavel even before the midpoint of the 114th: Both had visibly lost so much support within their own partisan ranks that their effectiveness was irreversibly imperiled. But, to be sure, the underlying reasons were very different. Wright, who was more feared than popular with his party, was undone by ethical lapses out of bounds for his times. Boehner, who remains more popular than feared within the Republican Conference, has been brought low by not aligning his political stripes to his times.

The three intervening speakers who also got pushed out of office ahead of their own schedule were shown the door for different reasons. But in each case, their miscalculations were soon magnified by intense public scrutiny and then exploited adroitly by the opposing party.

Wright’s successor, Thomas S. Foley, became the first speaker in 132 years to be defeated for re-election back home. He lost in Washington state in 1994 in part because he came across as oblivious to the warnings from fellow Democrats about the anti-Washington, D.C.-establishment mood of the electorate.

Foley’s successor, Newt Gingrich, was able to last only two terms as the first Republican speaker in 40 years. After barely surviving a coup plotted by the restive conservatives of his day, he felt compelled to give up his Georgia congressional seat at the end of 1998 to atone for his party’s midterm election setbacks after miscalculating the politics of impeaching President Bill Clinton.

Gingrich’s successor, J. Dennis Hastert, couldn’t hang on as a backbencher despite surviving longer as speaker than any other Republican in history. Having lost the top job when the party was ousted from power in 2006, he decided to quit his Illinois seat in the following fall, beleaguered and isolated by critics for countenancing misbehavior in his own ranks for too long and for appreciating the rise of small-government conservatism too late.

(Hastert’s own personal scandal came to light only this year. And he got to be speaker only because yet another person was pushed aside. Republican Robert L. Livingston was forced by the exposure of his moral failings to relinquish his Louisiana district just days before his formal elevation to the pinnacle of power.)

This roster of careers cut short leaves off just one speaker from the past 15 Congresses. Nancy Pelosi now stands out as not only the first woman to preside over the House, but also the first speaker since the mid-1980s who’s never lost control of her own political timetable.

The Californian’s extraordinary survival skills give extra weight to the warning she issued Friday to the next person put in charge over the House. The latest “seismic” upheaval, she said, means “the American people are even more closely watching what happens here next.”

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