"Don't swap horses in the middle of the stream"

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"Changing horses in the middle of the stream"
--Dan Fogelberg lyric, SOUVENIRS album, 1970-something.

     The Making of America database is helpful yet again.
     THE AMERICAN HERITAGE DICTIONARY OF AMERICAN QUOTATIONS (1997) has
"Don't swap horses" on page 383 as "ANONYMOUS, Republican presidential
campaign slogan, 1864. (...) This derived from a comment by Pres. Lincoln on
the inadvisability of changing horses in midstream..."
     This is from Gregory Titelman's RANDOM HOUSE DICTIONARY OF POPULAR
PROVERBS AND SAYINGS (1996), pg. 73:

_Don't swap horses in midstream._  Don't change leaders when they are in the
midst of important projects.  Probably originated in the United States.  Used
by Abraham Lincoln in his `1864 presidential campaign.  (...)  The main entry
is listed in all major dictionaries of American proverbs.  It is one of the
265 proverbs that every American needs to know, according to E. D. Hirsch, Jr.
1864.  I do not allow myself to suppose that either the convention or the
League have concluded to decide that I am either the greatest or the best man
in America, but rather they have concluded that it is not best to swap horses
while crossing the river, and have further concluded that I am not so poor a
horse that they might not make a botch of it in trying to swap.--Abraham
Lincoln, "reply to the National Union League."

     The following is from VANITY FAIR (a humor publication--it may have
invented these lines), 1862, pg. 50:

_Cabinet Conversation Pieces, No. 4_
(...)
PRESIDENT:  Not yet, Sir, not exactly yet.  What I said to the Boston
Delegation was: "Gentlemen; it ain't no time to swap horses when we are
crossing a torrent."
SEC OF STATE:  How grand that image!  No Sheik of the swift nomades of the
Eastern deserts ever let fall a finer metaphor than that "ere."
PRESIDENT:  Hear me through, Sir, if you please.  Says I, "It ain't no time
to swap horses when we are saddle-bags deep in a torrent..."