These days, Americans are pretty divided when it comes to politics. Opinions about President Trump are like night and day — Democrats loathe him, and Republicans love him. And political disagreements show up all over the place, including decisions about where to live. Naturally, these divides are reflected in elections, perhaps most noticeably in presidential contests, since voters turn out in greater numbers for them than any other races in the U.S.

If we look at the national popular vote margin of presidential elections since the end of the Civil War — the period in which the current two-party system largely took form (though the parties have certainly changed politically over the years) — we are currently living in the most competitive era of presidential politics.

The 2016 contest between Donald Trump and Hillary Clinton was the eighth consecutive presidential race in which the national popular vote margin was smaller than 10 percentage points. That is, in every presidential election from 1988 to 2016, the difference between the vote shares of the Democratic and Republican nominees was in the single digits. That’s the longest stretch of such elections since the Civil War, surpassing a run of seven straight single-digit margins from 1876 to 1900.

In the recent string of close elections, there have been two in which the nominee who won the national popular vote didn’t win the Electoral College — 2000 and 2016. Before 2000, the last time a candidate had won the popular vote but not the Electoral College was in 1888.

Now, some might not consider a large single-digit margin — such as Barack Obama’s 7-point win in 2008 — to be “close.” But it’s worth noting that out of 21 presidential elections from 1904 to 1984 — or the time between these two competitive periods — only nine had margins in the single digits. The other 12 were double-digit blowouts.

What was behind the competitiveness of presidential elections in the late 19th century and our current time? Most obviously, both eras featured high levels of political polarization and partisanship. According to VoteView.com, the largest ideological gaps between the two parties in Congress occurred at the end of the 19th century and around our present time. And recent data from the Pew Research Center shows that the American public has been becoming more politically polarized. Other research has found twin peaks in partisanship in the late 19th century and the current era, with highly nationalized elections that exhibited consistent voting patterns from state to state. It’s no coincidence that Electoral College maps in both periods often looked very similar from election to election.

Whether you like it or not, we are living in the longest era of highly competitive elections since the Civil War. Partisanship is strong, and opinions of the president are deeply polarized. This might be a sign that the 2020 presidential election will be close — and that the streak of single-digit margins in recent elections will continue.