Hillary Clinton's other historic hurdle: succeeding Obama as a Democrat

“Some of it is just the changes in the media and the visibility of the presidency that greatly expanded in the 20th century,” said Princeton historian Julian Zelizer. Television and other sources greatly amplified the presence of the president in Americans’ lives, he said, which in turn gave them more material to feel negatively about after eight years. Zelizer also said that in the last two or three decades the partisans for one party or another have become “very rigidified”, meaning every candidate and president faces “huge pockets of opposition even when they’re elected”. Those pockets could hold sway over the next election, he suggested.