John Boehner has been through debt-ceiling fights, a government shutdown, and increasingly bitter challenges to his authority. But never has his job as speaker of the House seemed to be in so much jeopardy as right now.

Top Republicans expect that one of Boehner's adversaries within the Republican conference will try to force a vote on whether to dump him from the speakership this fall, according to Politico. If he survives that, which might require support from some House Democrats, many Republicans think Boehner should or will step down at the end of this Congress.

On the surface, it's an odd fix for Boehner to find himself in: He came to Congress as a reformer and rose to the speakership as an antidote to the big-government conservative ways of leaders who pushed the No Child Left Behind and Medicare prescription drug programs into law. He's even presided over a permanent extension of most of the Bush tax cuts and significant reductions in federal spending.

But on a deeper level, Boehner has long been the last sentry for the party, using charm, strategic superiority, and his control over House rules to prevent the Tea Party wing from crashing through the gates of the establishment and putting Washington on total legislative lockdown. That has made Boehner the immediate proxy for the war grassroots conservatives are waging against the GOP's Washington insiders, and his enemies are emboldened by Donald Trump's ability to galvanize an anti-establishment fervor that shows no signs of subsiding.

Most ominously for Boehner, he will be faced with one of his toughest tests yet this month. If Congress doesn't act, the government will run out of spending authority on September 30. Some conservatives say they won't vote for a spending bill if it allows for federal funding of Planned Parenthood. Democrats in the House and Senate are dead set against eliminating funding for a women's health organization that provides cancer screenings, birth control, and STD tests with federal money and abortion services with private money.

That means Boehner is certain to be faced with the lose-lose choice of letting the government shut down over Planned Parenthood funding or risking the wrath of the rebels by allowing the funding to go through to keep the government operating.

The immediate threat to Boehner comes from a soft-spoken junior lawmaker from western North Carolina

In late July, Rep. Mark Meadows, a second-term congressman from North Carolina, introduced a resolution calling for a vote on whether to "vacate" the speaker's post — or, in plain English, to fire Boehner. The House quickly referred it to committee — or, in plain English, quashed it.

Meadows had chosen not to use parliamentary rules to force a vote, but the notice to Boehner was served: Conservatives have a mechanism for deposing him if they can round up the votes. If there were a vote, and no Democrats back Boehner, it would take only 29 Republicans to oust him.

Meadows has said that he would "certainly entertain" becoming speaker himself, and that he is confident that more than 29 Republicans would vote to oust Boehner.

If anything, Meadows has been emboldened during Congress's August recess, when he's had time to talk with his constituents about the frustration many Americans feel with their government and the House in particular.

"When they believe that their leadership is letting them down, there is only one option out there for us, and that’s to change that leadership," he said at one town-hall meeting, according to an excellent profile by the Washington Post's Mike DeBonis.

At times, Boehner has tried to strong-arm recalcitrant Republicans, including Meadows, by stripping them of subcommittee chairmanships, kicking them off committees and removing them from the vote-counting "whip" team. But those moves have engendered some backlash. Meadows won his subcommittee gavel back after it was taken away earlier this year.

The root of Boehner's trouble was evident before he became speaker

Boehner's relationship with the Tea Party wing of the GOP has always been an uneasy one. He kept Tea Party activists at arm's length until November 2009, when thousands of them congregated at the Capitol for a rally planned by a handful of House conservative gadflies.

Rather than get trampled by the parade, Boehner led House Republicans down the steps of the Capitol, waved a copy of the Constitution, and all but declared his allegiance to the Tea Party. At the time, the establishment and Tea Party wings of the GOP were united in their opposition to Obamacare, which was still making its way through Congress.

But rifts would emerge soon after Republicans won control of the House, and Boehner won the speaker's gavel, in the following year's midterm election. It was apparent at the time that he would have difficulty balancing the establishment's desire to govern with the Tea Party's impulse to tear down institutions.

In the summer of 2011, Washington was abuzz with talk of a $4 trillion "grand bargain" between Boehner and President Barack Obama. But the negotiations fell apart when conservatives in Boehner's own caucus whipped him back into line. Since then, he has struggled time and again to fulfill the basic obligations of government — funding federal programs and making good on debt — in the face of a rebellious phalanx of his caucus that telegraphs little pretense of thinking those are important goals.

That dynamic was never more evident than in the fall of 2013, when the government shut down over conservatives' insistence that a funding bill include provisions to delay implementation of Obamacare. Boehner had little choice but to go with his caucus. After more than two weeks of terrible press coverage, rank-and-file Republicans backed down, handing Obama a major victory.

History is repeating itself with the Planned Parenthood fight

Just like in 2013, a committed band of conservatives is insisting that Boehner refuse to keep the government running unless they are able to block funding for a program Democrats support. Last time, it was a massive government health insurance program. This time, it's federal subsidies for a single entity — Planned Parenthood.

Anti-abortion activists, and their representatives in Congress, are fired up about the program because of the release of undercover videos this summer that showed Planned Parenthood officials discussing the sale of fetal tissue. Several presidential candidates, including Trump and Sen. Ted Cruz (R-TX), have said it would be better to shut down the government than continue to give federal subsidies to the group.

So far, it's not clear whether House conservatives will have enough votes to prevent a spending deal that includes funding for Planned Parenthood.

Still, Boehner's handling of an issue that is central to the moral convictions of some of the members of his caucus could help determine whether he can survive the fall in power. If he misplays his hand, he could alienate lawmakers who are now inclined to side with him in a leadership fight.

Why it's so tough to stage a coup

For a mid-session coup to work, Boehner's enemies would have to deny him 218 votes on the House floor, and that could be a very tall order.

There are currently 246 Republicans in the House. The easiest way to win would be for all the Democrats and 29 or more Republicans to vote to "vacate" the speakership. It's possible, though certainly not assured, that some Democrats would come to Boehner's aid to offset Republican defections. But that would look terrible for the GOP.

So would the fight over replacing Boehner. In a party so badly riven that some of its members are considering dumping a leader who has presided over three straight electoral victories, it's hard to see who would emerge as a consensus successor. It could take many ballots for anyone to win 218 votes. And while it's far-fetched to think that a Democrat could become speaker, that fear was raised by Newt Gingrich's lieutenants when they plotted a failed coup against him in the 1990s.

It may be that the specter of an intraparty congressional brawl in the middle of a presidential election is enough to keep on-the-fence Republicans in Boehner's column.

There can be no doubt that Boehner has lost the confidence of a small but significant chunk of his caucus. But his saving grace may just be that there's no one capable of filling his shoes. Boehner has said before that he's "far from done" in the speaker's office.