What if Dan Sickles is on the Democratic Ticket in 1860?

https://en.wikipedia.org/wiki/Daniel_Sickles This was, actually, a quite real possibility, until Sickles gunned down his wife's lover, Philip Barton Key II, the Washington D.C. district attorney, and son of Francis Scott Key, the author of the lyrics to the Star Spangled Banner, the American national anthem, right in front of the White House. Somehow, that didn't quite have a "presidential ring" to it, although Sickles was acquitted, on the grounds of "crime of passion". Sickles was elected to the U.S. Congress in 1856, from New York, and was very popular and well known in his home state. He was considered a rising star in the Democratic Party, at the time, and was very well liked by, and well known to, President James Buchanan. Subsequent to his unfortunate assassination of the district attorney, he got himself made a general by raising his own brigade, and served as major general at the Battle of Gettysburg, where he lost a leg in battle. He is, actually, credited by many historians with actually having, personally, "won" the Battle of Gettysburg by quite systematically disregarding General Hooker's orders regarding the placement of his troops, and, he is accused of having almost lost the battle by many other historians, for exactly the same reason. So, suppose Sickles manages to defuse his wife's romantic entanglements without murdering the district attorney. As a popular New Yorker, he makes a credible and effective Presidential or Vice-Presidential pick, in 1860. The Democrats take New York in the 1860 election, and the Presidency, specifically because Sickles is on the ticket. Certainly, there will be no immediate Civil War, under these circumstances. What happens, exactly, next?