Which political leader was "attacked" by a rabbit?

That was Jimmy Carter. As if the poor man didn't have enough problems, becoming a laughing stock for being attacked by a rabbit didn't help.

Yep, it was Jimmy! Good answer, Jelp!
The 'attack' happened in 1979.
The rabbit incident happened on April 20 while Carter was taking a few days off in Plains, Georgia. He was fishing from a canoe in a pond when he spotted the fateful rabbit swimming toward him. It was never precisely determined what the rabbit's problem was. Carter, always trying to look at things from the other guy's point of view, later speculated that it was fleeing a predator. Whatever the case, it was definitely a troubled rabbit. "It was hissing menacingly, its teeth flashing and nostrils flared and making straight for the president," a press account said.

The article above, from straightdope.com, gives a possible explanation for the swimming rabbit. Since rabbits are not likely to swim, it says, it may have been a nutria. While nutria do not have ears like a rabbit, the 'face' of a nutria does resemble a rabbit, and nutria have large nostrils, which may account for the press account saying that the animal had "its teeth flashing and nostrils flared." Nutria are excellent swimmers.

"It's just a harmless little bunny isn't it?" in my best Monty Python and the Holy Grail voice.