Closest races won by each party?

[Tekken_Guy]

What will be the closest races won by each party in each chamber?

[Mr.Bakari-Sellers]

ME and IA Senate, Ds need to sure up IA and ME in case Tillis survives if the Senate comes down to a tie.

From that WI polls, the race is gonna close rapidly between Biden and Trump when then start surveying LV

As for the House CA 25 will once again be a battleground

[Roll Roons]

Senate: Closest D win is Kansas if Kobach is the nominee, Montana otherwise. Closest R win is the GA special runoff.  

House: Likely either a Clinton-won district with a strong GOP candidate (CA-21, CA-25, CA-48, FL-26, NJ-07, TX-07), a D-trending but R-held Texas seat (TX-21, TX-22 or TX-24). NY-22 will go to Trump again, but the GOP candidate is the same person who managed to lose it in the first place. IA-01 is a swingy district with a very good Republican candidate. So I think the closest D and R wins will be among these ten.

[Ferguson97]

Closest Democratic win in the Senate: Cunningham (North Carolina)

Closest Republican win in the Senate: Purdue (Georgia)

Closest Democratic win in the House: Eastman (Nebraska-02)

Closest Republican win in the House: Hagedorn (Minnesota-01)

[TrendsareUsuallyReal]

Senate: Closest D win is Kansas if Kobach is the nominee, Montana otherwise. Closest R win is the GA special runoff.  

House: Likely either a Clinton-won district with a strong GOP candidate (CA-21, CA-25, CA-48, FL-26, NJ-07, TX-07), a D-trending but R-held Texas seat (TX-21, TX-22 or TX-24). NY-22 will go to Trump again, but the GOP candidate is the same person who managed to lose it in the first place. IA-01 is a swingy district with a very good Republican candidate. So I think the closest D and R wins will be among these ten.

I’m a fan of these answers, with maybe NC being the closest D win if Kobach isn’t the nominee in KS. I’d also add a few more D-trending Texas seats like TX-2, TX-3, TX-10 and TX-31 to the list of House seats that could come out of nowhere and become nail biters. As of now, I expect Biden to win most of those.