This excerpt is from a walt whitman poem written in 1865. to what might the phrase "fearful trip" refer?

As the excerpt is not provided I looked it up and here is the excerpt:

"O Captain, my Captain! Our fearful trip is done; 
The ship has weathered every rack, the prize we sought is won."
- Walt Whitman, 1865

The answer is “Civil War”.

The fearful trip in this refers to the horrors and frights of Civil War. The author utilized a figure of speech to highlight the suffering and experiences during that war. It is reported that the poem was a dedication to Abraham Lincoln after his demise.

always include the steps and/or background required to get to the final answer. let’s other people understand and solve future problems on their own.

a is the final ! : )