My guesses, not strictly limited to the US:
Trump wins the nomination; establishment GOP disgusted but reluctantly accepts the hijacking of their party as the alternative to a Dem victory. Sanders has a good showing but still loses the nomination to Clinton. He eventually gives all his delegates and his endorsement to Clinton.
Trump wins significantly; he only gets stronger from controversy and scandal, while Clinton gets weaker. The next four years are awful; racists are emboldened, relations with countries around the world deteriorate, and the US goes to war with Iran.
In Europe, there is another major terrorist attack. Right-wing parties gain power in many countries. The UK leaves the EU, FN wins a lot of power in France in 2017, and the AfD get more seats in Germany. Overall, Europe is drifting significantly to the right. The war in Ukraine ends gradually as a frozen conflict; the rebel republics are de facto independent, war-torn, and run by warlords, while Ukraine remains embittered, impoverished, and dysfunctional. In the 2020's, President Nursultan Nazarbayev of Kazakhstan dies without a clear successor, having prevented the appearance of any. Kazakhstan has a disputed election; Kazakh nationalists make ethnic Russians nervous, and before long Russia moves in forces and annexes most of northern Kazakhstan. Other countries grumble at the illegality of it but do nothing. Putin is still president.
In the Middle East, the Islamic State smolders on, nobody able to fill the vacuum in the west of Iraq. Assad forms agreements to share power with FSA officials, then murders or imprisons them as soon as his position is secure again.
