I wanted to keep the discussion on the House and Senate races separate. The Presidential thread will be busy enough!

I'm not crazy enough to parse 435 House seats, but I did do the Senate races:

https://www.270towin.com/2024-senate-election/

"There are 34 seats up in 2024 - including a special election in Nebraska - of which 23 are held by Democrats or Independents."

AZ - Kyrsten Sinema - I - Not Running
Ruben Gallego - D - Seems likely to win. Lake is nuts.
Kari Lake - R

This wouldn't flip the seat as Sinema caucuses with the Democrats.

FL - Rick Scott - R
Debbie Mucarsel-Powell - D.
Rick Scott - Safe R.

Former RNC head Michael Steele says this is one to watch, Scott may be on the chopping block. Polling doesn't show that and with Trump having home state advantage, I don't see a split ticket there.

MD - Ben Cardin - D - Not Running
Angela Alsobrooks - Safe D.
Larry Hogan - R

MI - Debbie Stabenow - D - Not Running
Elissa Slotkin - Safe D.
Mike Rogers - R

MT - Jon Tester - D
Jon Tester - D
Tim Sheehy - R - Ahead in polling.

Likely flip D to R, despite the fact that Tester is well liked in MT. Polling is giving Sheehy the edge.

NV - Jacky Rosen - D
Jacky Rosen - Safe D.
Sam Brown - R

OH - Sherrod Brown - D
Sherrod Brown - D.
Bernie Moreno - R

Tossup. Brown leads in 4/5 polls, but it's a margin of error lead. Moreno is up in the most recent polling.

PA - Bob Casey - D
Bob Casey - Safe D.
David McCormick - R

TX - Ted Cruz - R
Colin Allred - D
Ted Cruz - Safe R.

Allred is up in only one poll, if the Cancun thing didn't sink Cruz, nothing will. Texas is gonna Texas.

WI - Tammy Baldwin - D
Tammy Baldwin - Safe D.
Eric Hovde - R

WV - Joe Manchin - I - Not Running
Glenn Elliott - D
Jim Justice - Safe R.

The following races are rated as safe for the incumbent party.

CA - Laphonza Butler - D - Not Running
Adam Schiff - Safe D.
Steve Garvey - R.

CT - Chris Murphy - D
Chris Murphy - Safe D.
Matt Corey - R.

DE - Tom Carper - D - Not Running
Lisa Blunt Rochester - Safe D.
Eric Hansen - R.

HI Mazie Hirono - D
Mazie Hirono - Safest D that ever D'd.
Bob McDermott - R

IN - Mike Braun - R - Running for Gov.
Valerie McCray - D.
Jim Banks - Safe R.

MA - Elizabeth Warren - D
Elizabeth Warren - Safe D.
John Deaton - R.

ME - Angus King - I
David Costello - D.
Demi Kouzounas - R.
Angus King - Safe I, Caucuses with D's.

MN - Amy Klobuchar - D
Amy Klobuchar - Safe D.
Royce White - R.

MO - Josh Hawley - R
Lucas Kunce - D.
Josh Hawley - Safe R.

MS - Roger Wicker - R
Ty Pinkins - D
Roger Wicker - Safe R.

ND - Kevin Cramer - R
Katrina Christiansen - D.
Kevin Cramer - Safe R.

NE - Deb Fischer - R
Deb Fischer - Safe R.
Dan Osborn - I

Osborn is making this a nail biter, but I don't see a steady red state going I.

NE - Pete Ricketts - R
Preston Love - D.
Pete Ricketts - Safe R.

NJ - George Helmy - D - Not Running, replaced Menendez.
Andy Kim - Safe D.
Curtis Bashaw - R.

NM - Martin Heinrich - D
Martin Heinrich - Safe D.
Nella Domenici - R.

NY - Kirsten Gillibrand - D
Kirsten Gillibrand - Safe D.
Mike Sapraicone - R.

RI - Sheldon Whitehouse - D
Sheldon Whitehouse - Safe D.
Patricia Morgan - R.

TN - Marsha Blackburn - R
Gloria Johnson - D.
Marsha Blackburn - Safe R.

UT - Mitt Romney - R - Not Running
Caroline Gleich - D.
John Curtis - Safe R.

VA - Tim Kaine - D
Tim Kaine - Safe D.
Hung Cao - R.

VT - Bernie Sanders - I
Bernie Sanders - Safe I.
Gerald Malloy - R.

WA - Maria Cantwell - D
Maria Cantwell - Safe D.
Raul Garcia

WY - John Barrasso - R
Scott Morrow - D.
John Barrasso - Safe R.

So...

Ind. -> D +1 (Sinema, no real change)
D -> R +1 (Montana)
Ind. -> R +1 (Manchin)
Tossup - OH

Ohio and Montana are going to be the races to watch. Right now, the Senate is split 49 Republicans, 47 Democrats, 4 Independents Caucusing with Democrats (Sinema, Manchin, King, and Sanders).

As VP, Harris casts the tie breaking vote which gives the Democrats the majority in the Senate, Committee controls, etc. etc. etc.

So if Montana flips. 50 R, 46 D + 4 I = 50. VP is the tie breaker.

WV flips with Manchin's seat going R. 51 R, 46 D + 3 I = 49. Democrats are out of the majority.

AZ flips with Sinema's seat going D. 51 R, 47 D + 2 I = 49. Doesn't change the math as Sinema caucused with the Democrats.

OH being the tossup, could be 52 R vs. 46 D + 2 I = 48. OTOH - Could be 51 R vs. 47 D + 2 I = 49. That would be a hold as that seat is currently D.

NE is a wildcard if it flips from R to I. 51 R vs. 46 D + 3 I = 49.

However you slice it though, it looks like Democrats will lose the majority in the Senate.