When everyone is in the same room they meet each other and then Travis tries to explain time traveling while they get into the machine.
As they left the time machine Travis tries to explain to the others, specifically Eckles so he can understand the butterfly affect.
As Eckels sees the T-Rex he starts to panic, wondering how he could of thought of killing it. Travis is also trying to tell him to go to the time machine before anything bad happens.
The T-Rex then attacks and Eckels stepped off the path. The others start to shoot the T-Rex and are surprised.
As everyone comes out of the time machine everything practically looks the same, but Eckels doesn't feel right, the air feels different, until he realizes the changes.
Something feels different.
When they all figure out that the presidential election is different and so are the words on the sign everyone gets upset, but mostly Travis. And in the end a sound of thunder is left behind because of Eckels mistake,