In Up Time (UT) USA?
Fun times!
1 - Most of the original 13 + plus Main, Vermont and Wee Vee, thus now known as the Lost Sixteen - are Dem voting states. USA politics are turned on their head. The 32 Senators from the DT states will make e.g. Woodrow Wilson look like a raging Wokeist.
plus
if Congress was in session - the top of the political and lobbist classes are gone.
2 - Wall Street gone. Such toxic institutions like Goldman Sachs - gone. Financial turmoil ensues.
3 - Economic turmoil accentuated by loss of industry. The country no longer has the capability to build nuclear carriers. Rebuilding such capacity will take how long - a decade?
4 - demographics quite different. Half of the Jews are gone. Almost half of Blacks are gone. USA is whiter, more Catholic, more Latino.
A small nit - the 1776 borders of the Original 13 are not identical to today's.
Meanwhile, in 1776 - there is more gold in New York than had been minded since the Dawn of Time. Several orders of magnitude more.
ADDED LATER:
In both timelines Montreal is washed away.
Jefferson and some other Founding Fathers are outraged: "What?!? You are saying I cannot breed my negro wenches and sell the brats down river? Outrageous Tyranny! To Arms, Sons of Liberty! Fight for your Property Rights!"
Any slave state that tries to stay out of the Union gets drowned in anti-slavery crusaders. This is too many peoples' berserk button and even if the government doesn't want to fight, civilian Americans have enough firepower in 18th century terms to pull a Texas.
The displaced 1776ers form one or two new political parties, but both initially caucus with the Republicans because at least the Republicans are mostly anti-abortion and anti-transgender.
The Army Corps of Engineers descends on Washington DC to drain the literal swamp that has replaced the metaphorical swamp and put up some temporary buildings because it's easier to rebuild a city than to select a new capital site.
Senate was in session but it was a non-legislative period. I'm not sure what this means, but I assume the senate minority and senate majority leaders would be attending.
schedule on p4
The House didn't have business scheduled on October 1st, but did on September 24 and October 4th. This is a large enough gap that I suspect most Representatives would have been in their home states.
Assuming all of the cabinet members in the presidential succession are ISOTed I believe Nancy Pelosi is president for what remains of Obama's first term. Since there are nine vacancies in the Supreme Court, this is the end of America. It's civil war o'clock. If the Senate lets her appoint even one justice there's a 100% Democrat court until the next election. She will use this to effectively ban all serious opposition parties because otherwise they'll form a coalition to stack the court and overturn Roe vs. Wade, which is fatal for the Democrat Party. Almost literally. If the unborn are ruled to be people abortion has always been murder (the ex post facto clause applies to congress not the courts, which inherently make ex post facto rulings) and the majority of the Democrat political class can be charged with conspiracy to commit murder for voting to fund or encourage abortion or donating to Planned Parenthood. Pelosi could go for a soft landing by appointing the Jay Court, letting them ban abortion, and immediately pardoning everyone, but I don't think she'd be willing to take that loss when she could try to appoint a court guaranteed to side her way on election challenges no matter the facts of the case.
All of this means the political violence doesn't stop until one side or the other is broken and the losing party is de facto banned under section 3 of the 14th amendment.
