Why is it so hard to be a Republican speaker of the House?

After an unprecedented vote in the House of Representatives, Kevin McCarthy was ousted as speaker. But he's not the first Republican leader to struggle to keep his caucus united, and if history is any judge, he won't be the last.

For 20 years, Democrats in the House of Representatives had one leader: Nancy Pelosi. In that same time frame, four different men led House Republicans: Dennis Hastert, John Boehner, Paul Ryan and Kevin McCarthy.

During Boehner's speakership from 2011-2015, he struggled to please Tea Party members who wanted to see him take hardline stances in negotiations. Ultimately, Boehner resigned mid-Congress in October 2015.

He was succeeded by Paul Ryan, who similarly struggled with the far-right members of the GOP caucus.

So why is it harder to be a Republican party leader?

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It comes down to one big issue splintering the party: spending. Some Republicans are willing to reform entitlements to save the government money. But to the American public, that's an unpopular way to reduce spending.

"It's virtually impossible for a Republican speaker to lead the whole caucus in a unified manner, because you're always going to have the tension between keeping the government running and cutting spending," said Brian Darling, a Republican strategist and former counsel for Sen. Rand Paul. "A good portion of the party doesn't want to tackle those difficult issues right now because they know, for many voters, it's an unpopular issue."

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Democrats can disagree too, but the divide just isn't as strong. However, Darling says the intra-party disagreement is a good thing.

"The tension in the party is going to continue to represent the will of the American people, because they want to see Congress cut spending, and they want to see one of the parties stand up for it," he said.

The House is expected to pick a new permanent speaker the week of Oct. 16, but regardless of who's leading the chamber, lawmakers have a lot to do in the next six weeks. And the same issues that almost caused a government shutdown at the end of September — border security, Ukraine assistance and budget cuts  — are likely to cause problems again.