I've thought about the possibilities of a second constitutional convention, for the second part of the TL. I don't think it could happen during the Civil War itself, when defending the Constitution and the legacy of the Founders became a big part of the rhetoric of the Union cause. But after the war I could see a Convention being called to propose reforms and, like the first, it ends up just rewriting the whole thing. I do believe certain changes are needed for the short-term success of reconstruction and long-term success of the nation. Among those I was thinking of was direct election of the President and Senators by a top-two run-off, changes in how the Supreme Courts works (term limits, different ways to appoint them, clarifying their powers), a line item veto for the President, term limits for the President, a clearer succession line, etc.
Lincoln did innovate in turning the focus of the Republican Party's source of claims of political legitimacy from the Constitution to the Declaration, in seeing within that earlier document a high moral standard of equality that even the Constitution as it was currently implemented had to yield to.
ITTL that has already changed since with the radical 13th amendment a future Congress can just declare gay marriage a right of the American people, and given that the amendment says quite clearly that the rights recognized in the laws of Congress cannot be denied, the power to force each and every State to recognize and perform gay marriages is there. So we already have a very important change in the history of American constitutionalism.
I think the biggest change is that Congress will be more willing to assert itself and its authority, especially with a friendly President. Though we now have a "Reconstructed Court" with a majority of Lincoln appointees, I can easily see Republicans arguing that they don't have to obey Supreme Court decisions regarding the constitutionality of its laws because then the SC is merely creating legislation - and only the sovereign will of the people represented in Congress may do that. The result may be a much weaker Supreme Court, at least for a few decades. Indeed, ITTL they may be remembered as merely pawns of Lincoln and Congress, because they are unlikely to try to oppose the President and Congress may just strip their jurisdiction if they step out of line.
I'm sure some Brits in this time would write some very smug articles about the Yankees finally appreciating the wisdom of parliamentary supremacy.
But yeah, I could see the Supreme Court as the first turkey on the chopping block if the nation reached the point of a constitutional convention. Dredd Scott freaked Northerners out as an unelected body, armed with powers that itgavd itself rather than receiving from the Constitution, seemed to threaten to basically invalidate a state's right to not have slavery. ITTL Americans may find judicial review an idea too useful to give up, but might create a new body, a constitutional court, to take over from what the old Supreme Court did in that capacity.
A form of class conscience that I hope to exploit more in the upcoming chapters is that often Northern soldiers took pride in being actual working men and denigrated planters as being inherently bad as a class. There are countless accounts of them being gleeful at the miseries of the slavocracy or boasting of the radical changes the war brought - a soldier for example wrote with joy of a slaveholder that tried to reenslave a person, only for them, "Northern mudsills" to throw him up in the air. Joined with the resentment of the Confederate poor this could become a crusade that seeks to destroy planters as a class before the South can be remade in the image of the free labor North. It could also lead to greater racial solidarity, as these White workers feel identified with Black workers as fellow victims of the aristocrats.
An obstacle to that North-South class consciousness of course was the different reactions of working class whites to the growth and encroachment of the industrial and capitalist free market system. As McPherson said in Battle Cry of Freedom, Whig and Republican support came strongest from those who felt they benefitted from the market economy, like socially mobile white collar labour and farmers near transport hubs who appreciated things like banks and railways and mines and factories. Even if you were a blue-collar man, this system could give you the skills and opportunity to rise in your station, with the Western frontier a recourse for people to save up money and head out to establish themselves. Meanwhile, Democrats found support among the outsiders of an increasingly commercialised and industrialised nation - artisans who resented being pushed to waged labour, or yeomen farmers who might be worried about larger markets driving up the prices of their needs and down the prices of their produce.
I like that idea, as the American Marseillaise. For that I actually found modified lyrics from a 1904 performance that I think fit better as a national anthem. Maybe, similarly to how the Philippines has a war flag and a peace flag, the US could have a war anthem and a peace anthem.
Yes we'll rally round - the flag, boys, we'll rally once again.
Shouting the battle cry of freedom
We'll rally from the hillside, we'll gather, from the plain
Shouting the battle cry of freedom.
Chorus.
The Union forever, hurrah boys, hurrah.
Bright in its glory shines ev'ry star.
While we rally round the flag boys, rally once again,
Shouting the battle cry of freedom.
We are springing to the call of our brothers gone before
Shouting the battle cry of freedom.
And we'll fill the vacant ranks with a million patriots more.
Shouting the battle cry of freedom.
Chorus.
Oh, then rally round the flag boys wherever it may wave,
Shouting the battle cry of freedom;
From the Northland,, tried and true, from the Southland ever brave,
Shouting the battle cry of freedom.
Chorus.
So we're springing to the call from the East and from the West,
Shouting the battle cry of freedom.
And if need be we will die for the land we love best.
Shouting the battle cry of freedom.
Hmm, the "boys" part may also require a change to be more inclusive.
How's this for a more gender-neutral version for the chorus and a verse, that keeps closer to at least how I would pronounce the syllables?
Out of many we are one, from the Mountains to the Main,
Shouting the battle cry of freedom.
None of us wear a crown, and neither will carry chains,
Shouting the battle cry of freedom!
The Union forever, unbroken and ours,
Hail to the banner, the Stripes and the Stars!
While we rally round the flag, oh rally once again,
Shouting the battle cry of freedom!