House Speaker John Boehner announces his resignation with tears in his eyes during a press conference on Capitol Hill on September 25, 2015. (Photo by Astrid Riecken/Getty Images)

John Boehner’s resignation underscores how divided the House Republican Party is right now. But it also reveals a deeper truth: the speakership has become one of the hardest and least secure jobs in Washington.

Quick trivia question: when was the last time a speaker’s tenure did not end in sudden resignation, because the speaker lost reelection, or because his/her party lost a majority of seats in the House? The answer is 1986 – nearly three decades ago.

Six fortunate souls have been speaker of the House since Tip O’Neill (D-Mass.) retired that year. Two lost the speakership when their party lost control of the chamber: Dennis Hastert (R-Ill.) and Nancy Pelosi (D-Calif.). A third, Tom Foley (D-Wash.), was not reelected to Congress. And three unexpectedly resigned: Boehner, Jim Wright (D-Tex.), and Newt Gingrich (R-Ga.). (Gingrich resigned at the end of the 105th Congress, arguably less disruptive than leaving mid-session, though it still came as a surprise.)

In other words, if you become speaker of the House, don’t expect a graceful exit.

To be sure, each of these speaker’s stories is unique. (Boehner may be the first in history whose departure can be connected, however remotely, to papal intervention.) But I think they collectively underscore two major reasons why the speakership has become a much harder job to hold onto.

First, party competition over Congress has become more intense. Since 1993, control of the House has switched from one party to the other three times (1994, 2006, and 2010), and the majority’s margin of control has often been quite narrow. That means today’s speaker may be tomorrow’s minority leader, or even a former member of Congress as in Foley’s case.

This competition also encourages members of the minority party to go after majority party leaders –even the speaker — in the hopes of tarnishing the majority party’s reputation. Wright and Gingrich were wounded by ethics investigations that were pushed by members of the minority party. Gingrich had spearheaded the investigation into Wright, which led to Wright’s resignation. Later, House Democrats eagerly returned the favor by going after Gingrich, who was reprimanded by the House but did not immediately quit.

As this “politics by other means” (as Ben Ginsberg and Martin Shefter called it) has become part of congressional life, they pose a peril for any speaker with something to hide.

Second, despite their incredibly high levels of voting unity, congressional Republicans have often been deeply divided, not only ideologically but also — and perhaps more so — over tactics and strategy. And it has become increasingly acceptable for Republican dissenters to seek to remove the speaker, something that used to be verboten.

Newt Gingrich was the first recent speaker to face the wrath of angry activists in his own party. During his second term as speaker he was threatened by a coup that involved several conservative “true believers” from the class of 1994 (as well as John Boehner, ironically). Though the coup failed, it left Gingrich weakened, and the threat of another internal challenge after the 1998 elections was enough to get him to quit.

As for Boehner, he was gradually worn down by a rump group of House Republicans who, while often agreeing with party leaders on policy goals, have insisted on a more aggressive, confrontational, “box canyon” approach to achieving those goals, even if they led to a government shutdown.

While watching his emotional press conference I was heartened to hear Boehner refer several times to the speaker’s job as being, first and foremost, to protect the institution of the House (something I have argued elsewhere).  And I would certainly urge Boehner’s successor to have the same goal.

But given how competitive Congress has become, and how divided the GOP seems to be, I expect he will end up worrying more about how long he’ll get to keep the speaker’s job. If history is any guide, it won’t be as long as he hopes.

Matthew Green is associate professor of political science at Catholic University. He is the author of “The Speaker of the House: A Study of Leadership.”