Misleading.
The North had a permanent lock on the House, and everyone knew it, as a result of preferential Irish and German immigration into the more temperate and healthier North.
Add more "freesoil" States, and voila. Permanent lock on the Senate, and soon -- following Lincoln's strategy of admitting undersized States like Nevada and West Virginia -- a host of new, small States full of freesoilers who'd vote to amend the Constitution to the Republicans' liking, at will, forever.
Oh, wait -- they did that, didn't they? Direct election of senators, and then the income tax, and then woman suffrage and Prohibition. Yup, that all worked out well, don't you think?
If Lincoln hadn't started and won the Civil War, we'd probably have had something like 54 instead of 48 States in "the lower 48".
Absent the rebellion, and had the existing slave states all hung together, then it would have taked 46 states to pass constitutional amendments the slave states opposed. That's a total of 61, if your math is weak. I guess they would still be working at it, huh?
Oh, wait -- they did that, didn't they? Direct election of senators, and then the income tax, and then woman suffrage and Prohibition. Yup, that all worked out well, don't you think?
Take a look at the ratification of those amendments and you'll notice that southern states were early and enthusiastics supporters of the 16th and 18th Amendments, and late out of the gate on the 17th and 21st. Reluctant support of the 18th would be, I imagine, to the southern preference for denying the vote to people.
If Lincoln hadn't started and won the Civil War, we'd probably have had something like 54 instead of 48 States in "the lower 48".
And still not enough to end slavery until Hawaii.