Dear what do you mean I'm less than b,
That's a really interesting question, actually. For those of you who aren't as familiar with the ins and outs of the U.S. Constitution as b and I are, the Three-Fifths Compromise is found in Article 1, Section 2, Paragraph 3, and it reads as follows:
Representatives and direct Taxes shall be apportioned among the several States which may be included within this Union, according to their respective Numbers, which shall be determined by adding to the whole number of free Persons, including those bound to a Service for a Term of Years, and excluding Indians not taxed, three fifths of all other Persons.
Simply put, only free people were counted when determining how many representatives each state would have in the House. Predominantly slave-holding states felt this was unfair, and wanted to have their slaves count toward that end. A compromise was reached in which three-fifths of the slave population of those states would count toward apportionment of Representatives. That was a good thing for those states, as many of them had large numbers of slaves, sometimes as much as nearly 50% of the overall population of the state. This gave those states more power in the House than they might otherwise have had, and possibly contributed to slavery persisting as long as it did.
So how would the election of 1860 have changed if those slaves had been counted as full people when apportioning out Representatives and votes in the electoral college? Well, to understand that, we'll first need to understand how the election looked in the first place. I've created a helpful map, which you can see below:
It's a commonly repeated fact that Abraham Lincoln won the 1860 election despite winning less than 40% of the popular vote and not appearing on the ballot in nearly any of the Southern states, but this map shows just how sizable an electoral victory he ended up with. His 39.7% of the popular vote translated into 180 electoral votes, more than the other three major candidates combined. John Breckinridge, the Southern Democratic candidate who supported expanding slavery into the western territories, won nearly all of the Southern states, just missing out on the Border states. Stephen Douglas actually came in second in the popular vote with 29.5%, but ended up with just 12 electoral votes (Missouri's nine and three of New Jersey's seven). Lincoln's support may have been sectional, but the fact is that with so many people living in the North, that section alone was more than enough to carry the election.
But remember, we're not counting 40% of the population of those Southern states. How would the electoral college look if we added them in?
It's actually a trickier process than it seems on the surface. Representatives are apportioned based on the population of their states, which we calculate every ten years during the Census. After those results come in, Congress will generally pass a apportionment bill that establishes the number of Representatives for each state. The 1850 apportionment bill, which was still in effect during the 1860 election, not only established those numbers, but also set a cap of 233 Representatives in the House, which was the current amount at the time. That means that until stated otherwise, when the House was reapportioned, there were a total of 233 seats to go around, so adding Representatives to one state required taking them from another. So if we're going to add Representatives to the South (and we'll need to, if we have an additional 40% of the population we need to take into account), we'll need to take them away from Northern states.
The numbers Congress may have come up with may have been different, but I think mine seem reasonable. I took the total population of the United States in 1850 (2,319,876) and divided it by 233 to see how many people each Representative would represent. That gives us 99,536 people, which I rounded up to 100,000 for simplicity's sake. For every 100,000 people in a state's total population, I gave them one Representative, generally rounding up. That means that Vermont, with an 1850 population of 314,120, got three representatives, while Rhode Island, with a population of 147,545 got two. After checking to make sure that I had a total of 233 Representatives and therefore 303 electoral votes (remember, Washington D.C. couldn't cast electoral votes for the President until the 23rd Amendment in 1961), I came up with the map below. This assumes every state still goes for the same candidate, since while we're counting the state's full population, we're still counting the same votes, since blacks (free or slave) weren't allowed to vote:
Some of the Northern states have fewer votes and some of the Southern states have more, but ultimately, it's not enough to really make a difference. Lincoln's electoral votes drop from 180 to 172, but he only needs 152 to win. He still has more than Breckinridge (79), John Bell (40), and Stephen Douglas (still 12) combined. So even if it weren't for the Three-Fifths Compromise, Lincoln would still have won comfortably.
But why stop there? We've already decided to count the South's slave population in apportioning Representatives. If we're going to count them as full people for the purposes of apportionment, why not count them as full people for the purposes of voting? Let's assume that all of the slaves in the South are allowed to vote for whichever candidate they choose.
To figure out how that would change the election, we're going to have to make a few assumptions. First, we're assuming that not only are the slaves allowed to vote, they're allowed to vote free of pressure or harassment. That's a brave assumption, given the wave of Jim Crow laws that prevented blacks from voting freely in the South for generations, as well as general intimidation practices. But since we're already rewriting history, let's go ahead and rewrite it so that they can vote freely. Determining who they'll vote for is trickier still. We can't just look to the North for general voting trends, since blacks weren't allowed to vote anywhere in the U.S. during the 1860 election. We could look at future elections, but that only gives us a sense of party loyalty. A person voting for Ulysses Grant in 1868 wouldn't necessarily have voted for Lincoln in 1860 any more than a person voting for Barack Obama in 2008 would necessarily have voted for Al Gore in 2000.
We're going to have to be a little reductionist here. For the purposes of this thought experiment, I've decided that slaves are going to be single-issue voters, and that their single issue is going to be slavery. The Republican party wasn't as overtly abolitionist as it was in 1856, but it was at least sympathetic to the cause. Lincoln is probably going to be the top choice of slaves in 1860. Douglas and Bell were neutral on slavery, and as mentioned earlier, Breckinridge supported spreading slavery into the Western territories, even in cases where those territories' populations didn't support the practice. (It will come as no surprise to you, I'm sure, that Breckinridge served as a general in the Confederate army after he lost this election.) I'm assuming that when slaves are allowed to choose between these four candidates, 80% of them are voting for Lincoln, 10% each are voting for Douglas and Bell, and 0% will vote for Breckinridge. An inexact method, to be sure, but since we don't have any sort of polling data on the subject, it'll have to do.
Of course, as we mentioned earlier, Lincoln didn't even appear on the ballot in many of the Southern states. (Nor did Breckinridge in many of the Northern states, for that matter.) I decided that in states without Lincoln on the ballot, slaves would split their vote 50-50 between Douglas and Bell, and in cases where Douglas wasn't on the ballot either, slaves went 100% for Bell.
The last bit is the easiest. While we're extending suffrage to the slaves, we're also assuming that not all of them are going to be able to or choose to vote. Voters still have to be over 21 and male to vote in this election. A quick look at the 1860 Census shows that about 44% of slaves were 21 or older at the time, and about half of them were male. Voter turnout was 81% in the 1860 election (one of the highest in history!), so only 17.8% of slaves are actually going to end up voting in the Southern states. We're keeping the apportioned votes the same for this, as you can see below:
Looks quite a bit different, doesn't it? Lincoln still carries the North handily, and in this case, he very nearly wins Virginia, too, taking 80% of the state's 87,473 voting slaves. (Consider that Bell actually won the state with 74,481 votes in 1860. That's an awful lot of disenfranchised voters.) In fact, with Breckinridge not receiving a single slave vote, he loses all of his states except for two, and he probably only wins South Carolina because at the time, its electoral voters were appointed by the state legislature rather than determined by the popular vote. It wouldn't have mattered how many slaves were voting if the legislature was unchanged. (Of course, if slaves were permitted to vote, the legislature may have had an entirely different makeup.) Bell carries most of the South due to picking up the slave vote. And it doesn't make an ounce of difference, because Lincoln still has 172 electoral votes to Bell's now 107. He's still our President.
Of course, had slaves been given a full vote, everything would been different. Maybe they have a chance to effect some real change in government. Maybe these four candidates stand for different things. Maybe different candidates for the presidency emerge. There's lots to consider. Political science is a complex field with lots of variables, like you said. But even if we don't and can't take all of them into account, it's still fun to think about how things might have turned out differently, isn't it?