Personally, I think even waiting til reconstruction was a mistake.

I get not wanting to accept any validity to the confederate state’s secession, and therefore have them maintain statehood after the war as opposed to becoming US owned territories.

But, imo, the moment the war started, congress should have been convened, and the constitution amended to dissolve the senate, which was only created to give power to the southern states, giving ‘land a vote’. Likewise, it should have been amended to force all state governments to do the same, by mandating all state legislative bodies be unicameral, and comprised solely of representatives representing an equal number of citizens.

In doing so, after the war, the freed slaves would have constituted a strong majority over the remaining white men, and the union states a strong and enduring majority in the US congress.