Were now less than a week away from the Iowa caucuses, and the contest there can best be described as a four-way race. As of Tuesday morning, former Vice President Joe Biden, Sen. Bernie Sanders, former South Bend, Indiana, Mayor Pete Buttigieg and Sen. Elizabeth Warren were all clustered within about 8 percentage points of each other in our average of the states polls, with Sanders and Biden at 22 percent, Buttigieg at 17 percent and Warren at 14 percent.

Given just how close things are in Iowa, our forecast doesnt give anyone more than a 36 percent chance of winning the caucuses next week. This got us thinking: How unusual is it for the field to have this many candidates within a few points of each other? Answer: Its pretty unusual.

[Our Latest Forecast: Who will win the Iowa caucuses?]

Number of candidates (including the leader) within 10 points of the lead in Iowa a week before the caucuses, in FiveThirtyEights polling averages

Excludes cycles for which we have insufficient polling data.

Source: Polls

Using our forecasts historical Iowa polling averages from the week before the caucuses in each presidential election since 1980, we found that the 2020 contest not only has the largest number of contenders within 10 points of the polling leader, but also is tied for the most candidates polling at or above 15 percent, with one candidate polling just under that threshold. As you can see in this table, while there were three candidates within 10 points of the Iowa leader (counting the leader themselves) in both the 2008 Democratic primary and the 2012 GOP primary, theres never been a primary where four candidates were clustered so tightly until 2020.

This isnt to say the 2008 and 2012 contests werent nail-biters in their own right. In the 2008 Democratic contest, then-Sen. Hillary Clinton was in first, averaging 30 percent in the polls a week before the caucuses, while then-Sen. Barack Obama had 26 percent and former Sen. John Edwards had 22 percent. And four years later in the 2012 GOP race, Rep. Ron Paul and former Gov. Mitt Romney were essentially tied at about 21 percent each, while former House Speaker Newt Gingrich had about 15 percent.

The top Iowa polling average and the number of candidates polling 15 percent a week before the caucuses, in FiveThirtyEights polling averages

Excludes cycles for which we have insufficient polling data.

Source: Polls

But even setting aside that there are more competitive candidates in Iowa this year than ever before, there are two other things that make the 2020 Democratic race in Iowa especially close. First, Sanders, whose Iowa polling average is just a hair ahead of Bidens, isnt polling that high for a front-runner. At 22.6 percent, he has the second-lowest polling average for a leading candidate one week before the caucuses. (Paul sat at 21.5 percent in 2012.) Second, there are three contenders polling above 15 percent, which is tied for the most candidates in any presidential election cycle.

But a fourth candidate, Warren, is just short of the 15 percent mark, so this years caucuses could produce a historic result: Since the start of the modern primary era theres never been a major-party contest in Iowa where more than three candidates won at least 15 percent of the vote statewide. Moreover, since 1992, when the Democratic Party implemented some of the rules that continue to define its nomination races, there has not been a single Democratic primary or caucus in any state or territory in which more than three candidates have won at least 15 percent of the vote statewide. Although Warren has fallen slightly below the 15 percent mark, she also just got an endorsement from the Des Moines Register, which might help her reverse her polling slide in the state. So if Sanders, Biden, Buttigieg and Warren all go on to finish above 15 percent, it would be a first.

However, the Democrats caucus rules could make it tough for four candidates to clear that 15 percent bar. In each precinct, candidates must clear a viability threshold, typically 15 percent of the votes at the caucus site, in order to advance. If they arent able to clear that bar, their backers are asked to realign themselves to candidates who do.

So you could imagine a situation where a candidate polling around 15 percent in Iowa (Buttigieg, Warren) doesnt actually earn 15 percent of the vote statewide next Monday because they fall short of the viability threshold at a number of caucus sites, causing their supporters to move to other candidates and their overall numbers to fall. Yet despite that hurdle, its still plausible that Biden, Buttigieg, Sanders and Warren all have enough second-choice support to end up above 15 percent statewide a New York Times Upshot/Siena College poll of Iowa released on Saturday found that all four candidates surpassed 15 percent when respondents had to choose among just that quartet of candidates. Remember, though, that there are many more candidates in the race. And some of them, especially someone like Sen. Amy Klobuchar, whos polling at just shy of 9 percent in Iowa, could throw an interesting curveball in the realignment process.

Of course, Klobuchar (or another candidate) could also surge here in the last week, throwing a real wrench in our analysis. This kind of surprise, last-minute surge has actually happened before. In 2012, former Sen. Rick Santorum averaged only 7 percent in the polls a week before the Republican caucuses granted, he had been steadily ticking upward in the preceding month yet he not only surpassed 15 percent statewide, he won Iowa by a handful of votes.

Another challenge in our analysis is that some older election cycles just dont have that much data to work with. For example, there were only two polls from the 1996 GOP race that were conducted between one and five weeks before the caucuses. And we dont have a polling average for the 1992 Democratic race because there werent enough polls available, although the 1992 caucuses were also kind of unusual because they werent considered competitive Iowa Sen. Tom Harkin had a massive home-field advantage (he won in a landslide).

But despite those caveats, the data we do have suggests that this years caucuses may be the most competitive and crowded Iowa has ever had. There are more candidates polling within 10 points of the leading contender than in any race since 1980 and a record-tying number of candidates polling above 15 percent, with another just below that mark. Whether one candidate will get a late boom or bust remains to be seen, but with a week to go, no candidate is close to being a clear favorite. That makes for an exciting and potentially unpredictable finish, so get ready for the final sprint.

More here:

Why These Might Be The Most Competitive Iowa Caucuses Ever - FiveThirtyEight