What does the phrase, "swapping horses in the middle of the stream, "mean, and who said it?

a.)lincoln said it & was referring to his disapproval of changing the presidential administration during the civil war

b.)california journalist noah brooks said it was referring to electing a president during the southern sates secession ***

c.)george mcclellan said it and was referring to the inability to fight simultaneous battles with the north during the civil war

d.)john fremont said it and was referring to lincoln's failure to maintain union battle victories during his presidency