Barack Obama is the most polarizing president since the birth of modern polling — Democrats love him, and Republicans can't stand him. But the partisan split in approval of Obama is the culmination of a trend that's been building for decades, as you can see here:

Here are a few points worth noting about this chart:

Partisan differences in evaluations of presidents have existed for decades. But the gap between Democrats' and Republicans' evaluations of each president used to be 30 to 40 points — and now it is consistently much higher, from 50 to nearly 70 points. To get a partisan gap that huge, a president's approval among his political opponents basically always has to be in the toilet, and approval among his supporters must always be quite high. The increase in polarization seems to begin with Ronald Reagan — and it's partly because Republican voters were tremendously enthusiastic about his presidency. He averaged 83 percent approval among GOP voters, much higher than the previous four presidents did. But this wasn't accompanied by a corresponding surge in support from Democrats. The trend doesn't end with Reagan, though — every president since has topped 80 percent approval, on average, among his own party's voters. Recent presidents have been very good at retaining the support of their bases. George HW Bush was the last president to amass a pretty strong approval rating among the opposite party, with 44 percent of Democratic voters approving of his performance. But this overall average combines Bush's very high approval in his first few years (with the end of the Cold War, and the successful Gulf War) with a massive dropoff in his final year. You can see at Pew that this approval collapse in 1992 was particularly concentrated among Democrats, and helps explain why Bush failed to win election. Finally, Bill Clinton, George W. Bush, and Barack Obama each posted new lows in average approval among voters from the opposite party, while retaining over 80 percent average approval among voters from their own party. Obama's partisan gap of 67 points is the biggest of all.

It's important to remember, though, that modern polling only goes back to the mid-20th century. As President Obama pointed out when Vox recently asked him about this topic, there were many extremely polarized periods in American politics before that — like the Civil War. Watch Obama's assessment of why his presidency has become so polarizing below: