One graphic that explains how brokered conventions work — and why they're so unlikely

A brokered convention is a favorite subject of election-year media speculation.

Every four years, the chatter begins in earnest over the winter: Will this be the year that party elites, through backroom deals, end up picking their own, favored candidate?

This year, the chatter began after the Washington Post reported in December that Republican Party elites held a secret dinner meeting to discuss what would happen if Donald Trump arrived at the convention with a significant number of delegates.

Brokered conventions make for good headlines. They just sound dramatic and exciting, with campaigns trying to woo delegates, secure votes, and come out of the convention triumphant. And when they do happen, they really are exciting! Exhibit A: In 1924, it took Democrats 103 rounds of voting to finally pick their nominee. The whole affair took two weeks, the longest nominating convention in American history.

"If no nominee is elected after first ballot, all hell breaks loose," says Elaine Kamarck, author of Primary Politics: Everything You Need to Know About How America Nominates Its Presidential Candidates. "An old-fashioned, complex negotiation process takes place where you see party chairmen playing a very big role in who becomes the nominee."

But brokered conventions are also incredibly unlikely. A brokered convention occurs when no candidate earns 51 percent of the vote, or a simple majority, on the first ballot. This hasn't happened in either party since the 1952 Democratic convention, and primary election reforms, which passed in the late 1960s, make it especially unlikely that 2016 will be the year that changes that.

To understand why, it's important to know how brokered conventions work — and why that makes brokered conventions so uncommon today.

Up through the mid-20th century, brokered conventions were relatively common. Party elites pretty much controlled the nomination system, leaving the general public largely in the dark. Some states held primaries; others didn't. That would leave the decision of whom the states' delegates would vote for largely up to local political leadership.

There weren't any rules about whether delegates actually had to vote for whom they'd been told to support (that's since changed — more below). So there were fewer barriers to convincing delegates to change their minds.

Take 1948, when then–New York Gov. Thomas Dewey sought his second bid at the Republican nomination (he lost his first bid in 1944 to Franklin Roosevelt). After three rounds of voting, Dewey and his allies were able to woo enough delegates to clinch the nomination. Although, as the infamous photo reminds us, Dewey's efforts were ultimately for naught — he was unable to defeat Truman.

Deals like this made the primary process seem especially undemocratic. If primaries played a minor role and delegates could switch their votes at a whim, what was the point of the nominating convention in the first place?

Everything about primaries changed in the 1960s

Primary reform in the United States arguably began with the Vietnam War.

In 1968, Sens. Eugene McCarthy and Robert F. Kennedy both ran on anti-war platforms against then–Vice President Hubert Humphrey.

Together, McCarthy and Kennedy won more than two-thirds of the votes in primary contests, while Humphrey didn't even participate in the primary process, declaring, "Any man who goes into a primary isn't fit to be president." But in 1968, only about 40 percentof delegate votes were decided through popular vote — the rest of the delegates were free to make up their own minds about whom they wanted to support. And in 1968, they helped Humphrey clinch the nomination.

McCarthy and Kennedy supporters were outraged and protested the result. This led the Democratic Party to overhaul the presidential nomination system with the McGovern-Fraser Commission in preparation for the 1972 Democratic convention. Republicans did not form their own commission but followed suit, enacting many of the reforms pushed forward by the Democratic commission.

First, primary election results became binding on delegates. Before, state delegates could view their states' votes as something akin to a recommendation. But now they were obligated to actually vote with them. This rule significantly reduced the possibility of a brokered convention, because now most delegates' votes were spoken for in advance of the convention. Candidates seeking the nomination now could better understand where they stood in relation to their competitors.

This still holds true for at least the first round of a convention. If a brokered conventionwere to occur, delegates could change their vote as they saw fit. Some states have binding laws for their delegates, but Kamarck said that quite frankly "the law goes out the window."

Second, new rules required primaries to be held on the same day throughout the state. Prior to the reform, caucuses sometimes lasted three to four weeks and weren't covered as news stories, largely because they weren't on the public's radar.

"Now you could immediately look at caucuses as discrete events, which was a big change," said Kamarck. "You could now look at Iowa on caucus night and see that Jimmy Carter won, which made for a news story."

Additionally, Kamarck stressed that it was the increase in the number of primaries that ultimately transformed the primary system from political backroom dealings into a very public system. The number of presidential primaries in 2012 was 38, more than double the number of primaries held in 1932. The other 12 states and respective US territories hold caucuses.