Seeking help identifying a time travel story from (I think) the 1970s

Question

I read this story sometime in the '70s in one of the prozines of the time, but it might have been a reprint or just from an older issue acquired in a used bookstore....

There's been some kind of apocalypse with just a few survivors, who are capable of psychic time travel. They can only visit times from before when each was born, and the time stream keeps compensating for whatever changes they make. Each one is pursuing some kind of pet project - one is trying to keep Lincoln from being assassinated, and another remarks that when he hears people later in the 19th century talking about "Ape Lincoln", he knows that the first has succeeded, but the changes are always overwhelmed.

One of the characters works out a very elaborate scheme requiring all of them making changes that'll reinforce each other enough to make a lasting change, but it doesn't work, either.

Help, please, if you can. :)

Answer 1

It's The Tides of Time by Gordon Eklund - Galaxy March 1977.

“And you ought to leave poor Lincoln alone, too.” She seemed full of suggestions today. “I can always tell when you’ve been around, when people start talking about Ape Lincoln instead of the Great Martyr.”

and later

The roll of paper lay open upon the floor. He looked.!It seemed to be some sort of historical chart. Dates ranging from 4500 B.C. through 1996 A.D. were printed across its top, while underneath were various notations. He read one that concerned him particularly:1865 Lincoln not assassinated; Lee appointed to cabinet;freemen suffrage voted down.“What’s this for?” he finally asked.