That would be the same Congress that had 23 southern House speakers from the south compared with 12 from the North? The same Congress that had 24 Senate President Pro-tems from the south vs. 11 from the North. The same region who had held the presidency for 60 out of 84 years? If the slave states weren't defended to their satisfaction then who do they have to blame but themselves?
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".