This post is part of Polyarchy , an independent blog produced by the political reform program at New America , a Washington think tank devoted to developing new ideas and new voices.

Every now and then in American politics, political parties enter their presidential nominating conventions deeply, deeply divided. And when they are deeply divided, they lose.

Conventions, rather than being coronations, turn into battles between rival factions, each with a legitimate hope that it will somehow come away from the convention with its candidate as the nominee. But in the end, the party can only choose one nominee, and thus only one faction can win. That means the other faction goes home dejected and angry. Some of them will vote for another candidate. Some won't vote at all.

This is the Republicans' problem in 2016. At this point in the game, it's increasingly clear the Republican's July convention will be a barnburner of fights to rival the most bitter of conventions, with wounds that will probably take years, not months or weeks, to heal. And whomever the delegates ultimately choose, there is no consensus candidate left. The divisions have grown too deep.

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What history tells us: Divided conventions produce general election losers

Depending on how you count it, since 1900 one party has been much more deeply divided than the other party between seven and 10 times. In a few of those years, both parties were at least somewhat divided. But in all 10 elections, the party that was more deeply split lost the general election.

Each election is obviously different. But looking across the elections, two general patterns emerge.

First, an internal fight is almost always a sign of deeper party weakness. Fights emerge either because the party is deeply split between two or more internal factions or because the leading nominee (sometimes the incumbent) is already weakened, and others see an opportunity. Either way, it's bad news for that party in the general election.

Second, conventions don't heal divisions. In the bitter fight over the nomination, nobody comes out looking particularly good. If one faction wins, the other loses. And that means voters who are so angry and disappointed that they're either going to stay home or vote for a third party (divided major parties often invite third-party opportunists). They might even vote for the opposing party.

Maybe history will be different this time. But it seems unlikely.

So here are seven times parties have been deeply divided going into their conventions, including two since parties adopted the modern binding primary election system in 1972. (Before that, primaries were not binding.)

1) Republicans, 1912

In 1912, Teddy Roosevelt, who had promised not to seek office again after winning the 1904 election, decided that President Howard Taft had betrayed TR's progressive legacy and the Republicans needed to nominate Teddy.

Roosevelt stormed the country in the primaries, demanded Republican delegates at the convention nominate him, and then, when the delegates stuck with Taft (who was, after all, the incumbent), ran as a third-party candidate, splitting the Republican vote and throwing the election to Democrat Woodrow Wilson.

Of course, we might note that Democrats were also somewhat divided that year — it took Wilson 46 ballots to get the nomination. But Republicans were far more divided.

In November, Wilson won in a landslide, securing 435 electoral votes to Roosevelt's 88 and Taft's 8 and winning 41.8 percent of the popular vote to Roosevelt's 27.4 percent and Taft's 23.2 percent.

2) Democrats, 1924

In 1924, Democrats were deeply divided (as they had also been in 1920). William G. McAdoo, a Georgian, had been Woodrow Wilson's Treasury secretary. He was a prohibitionist and a member of the Ku Klux Klan, with strong support from the party's Southern wing. Al Smith, the governor of New York, was an anti-prohibitionist, anti-Klan Catholic with strong support from the party's Northern wing.

For 102 ballots, party delegates argued over which should be the party's standard-bearer. On the 103rd ballot, Democrats finally settled on John W. Davis, an anodyne lawyer who had been Wilson's solicitor general. He was uninspiring at best as a general election candidate.

In November, Republican Calvin Coolidge won in a landslide, getting 54.0 percent of the popular vote to Davis's 25.6 percent. Davis did, however, win the South, getting 136 electoral votes. But Coolidge got 382. Progressive Robert La Follette got the remaining 13 electoral votes, along with 16.6 percent of the election.

3) Republicans, 1948

Republican delegates were split between the more conservative Ohio Sen. Robert A. Taft (a.k.a. "Mr. Republican") and the more liberal New York Gov. Thomas E. Dewey. It took three ballots for Republicans to nominate Dewey.

Of course, one could call 1948 somewhat a wash, since in 1948 Southern delegates walked out of the Democratic convention when Hubert Humphrey gave a major speech on civil rights, and Southerners nominated Strom Thurmond to run as a "Dixiecrat" on the "state's rights" ticket, winning four Southern states. Still, Democrats were probably more unified. Truman, though unpopular, was their incumbent, and the Southern splinter group was a small fraction of the Democratic constituency.

In November, Truman won a surprise victory, getting 303 electoral votes to Dewey's 189 and 49.6 percent of the popular vote to Dewey's 45.1 percent.

4) Republicans, 1964

Republican voters were split between the more moderate wing of the party, represented by Pennsylvania Gov. William Scranton, and the more conservative wing of the party, represented by Barry Goldwater. Despite pleas by New York Gov. Nelson Rockefeller for himself or the more moderate Scranton, Goldwater forces had out-organized the moderates and controlled the delegates. Goldwater won on the first ballot, and in his convention speech uttered his famous line, "Extremism in the defense of liberty is no vice. And moderation in the pursuit of justice is no virtue."

The incendiary speech did not heal the party divisions. The Republican Party went into the 1964 general election deeply divided.

In November, Democrat Lyndon Johnson won in a landslide, with 486 electoral votes to Goldwater's 52 and 61.1 percent of the popular vote to Goldwater's 38.5 percent.

5) Democrats, 1968

It was a wild year in American politics. Early in 1968, Lyndon Johnson announced he would not seek reelection, opening up the Democratic nomination. Eugene McCarthy emerged as early antiwar candidate and favorite of student activists. Robert F. Kennedy also entered the race as an antiwar candidate but was assassinated in June, just after winning the California primary.

Hubert H. Humphrey, the vice president, was the clear choice of most party regulars and selected by the delegates. But antiwar protestors disrupted the 1968 hoping for McCarthy, and the Democratic Party came away from the disastrous Chicago convention a deeply divided party.

Arguably, the Republican Party was still somewhat divided in 1968 between Richard Nixon (the eventual nominee) and Nelson Rockefeller, who represented the shrinking moderate wing. The more conservative California Gov. Ronald Reagan also tried to make a bid for the nomination, but Nixon won easily on the first ballot.

The 1968 election also included the third-party run of George Wallace, the Democratic segregationist governor of Alabama. Southern segregations has been alienated from the Democratic Party but not yet incorporated fully into the Republican Party.

In November, Nixon defeated Humphrey, winning 301 electoral votes to Humphrey's 191 and 43.4 percent of the popular vote to Humphrey's 42.7 percent. Wallace won four Southern states (46 electoral votes) and 13.5 percent of the vote.

6) Republicans, 1976

Gerald Ford, the Republican incumbent, came into the convention with the most delegates and the most primary votes. But Ronald Reagan had come very close, and had picked up momentum later in the primary season. Neither had the requisite majority. Both fought hard for the uncommitted delegates, and Reagan tried, unsuccessfully, to get some rules changed to help him. But Ford won, narrowly. Reagan's acolytes were not happy. In November, Carter bested Ford, winning 297 electoral votes to Ford's 240 and 50.1 percent of the popular vote to Ford's 48 percent.

7) Democrats, 1980

Coming into the 1980 convention, incumbent Jimmy Carter had the delegates. But Massachusetts Sen. Ted Kennedy had waged a tough primary battle, and wasn't done yet. He tried to change the rules to unbind delegates. He failed. Carter was not beloved among Democrats, one reason why Kennedy had challenged him in the first place. The challenge did nothing to heal the wounds.

In November, Reagan won in a landslide, getting 489 electoral votes to Carter's 49 and winning 50.8 percent of the popular vote to Carter's 41 percent.

Arguably, this list of divided parties could also include Democrats in 1920 (when it took 44 ballots to nominate James M. Cox, though Republicans were also somewhat divided that year — it took 20 ballots for Republicans to get to Warren G. Harding); Democrats in 1952 (when it took three ballots to nominate Adlai Stevenson, though Republicans also had a fight that year, so maybe 1952 is a wash); and Democrats in 1972, when anti-McGovern forces tried to mount credential challenges to Democrats.

In all three years, Democrats lost by wide margins. If we added these conventions, very divided parties would be 0-10 in general elections since 1900.

History says: Republicans are too divided; they will lose in November

Obviously, there are other factors that determine electoral outcomes. There is a cottage industry of models that predict outcomes based on how the economy is doing, the incumbent party's popularity, how long the incumbent party has been in office, and some other factors.

These models generally do a good job. And they don't necessarily conflict with the party division argument, since parties in weak electoral positions are generally more prone to internal division. But when a statistical model predicts a Trump victory with 97 to 99 percent certainty, it's worth questioning that model.

After all, the basic pattern I've described here holds with remarkable consistency. Parties that are deeply divided going into their conventions do not win general elections. Parties that are somewhat divided can only hope that the opposing party is more divided.

Certainly, one could argue that back in the 19th century, when brokered conventions were the norm, contested conventions didn't hurt parties' general election chances. But politics has changed considerably since then. In modern times, a split party spells electoral defeat.

And admittedly, the quantitative political science literature finds a more mixed general election effect for party "divisiveness" in primaries. But I'm arguing here for a more qualitative understanding of divisiveness, one that's more measured by how contested the convention is rather than how closely fought the primaries are.

Given the deep divisions within the Republican Party, it's hard to see how the factions meaningfully unite in Cleveland. If history is any guide, Republicans will head into August in deep trouble. And unless Democrats have an even bigger internal fight (very unlikely at this point), Democrats will win in November. Maybe history will be different this time. But I wouldn't bet on it.

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