There are basically 11 contested senate races this cycle, listed below with the state's partisan lean (Cook, via Wiki). WV is lost so Dem need to win 9 to get to a 50-50 tie.
The Dems are doing really well due to a combination of good candidates and strategy and republican stupidity. They lead in 8 so they need to get one of FL, TX, MT.
Lean Comments (average of polls from 538; ++ = quigley donated)
MD D+14 Former popular Rep vs Dem Alsobrooks; Dem up but limited polling --> watch out here
NM D+3 Incumbent Heinrich-D lead is ~ 6 over daughter of former Rep senator --> watch out here
MI R+1 Slotkin-D up 3-5
NV R+1 Rosen-D up 5-8, wide poll results in hard to poll state
AZ R+2 Gallego-D up ~ 6; bad R candidate; ++
PA R+2 Casey-D up 6-8
WI R+2 Baldwin-D up ~ 7
FL R+3 Mucarsel-Powell-D down 4; Rep candidate with tons of $; ++
TX R+5 Cruz 3-4; ++
OH R+6 Brown-D up 5-6; ++
MT R+11 4 of 5 polls Tester-D down; only 1 quality poll, Emerson, Rep +2; ++
Here's why you should focus your attention on Senate races, particularly FL and TX:
1. Harris-Walz will win, but if they don't, we're screwed anyway.
2. Harris has to show results and will need a trifecta to do so. House should be carried to Dems by Harris's coattails.
3. Brown and Tester are great (esp Brown), but they will be last Dem Senators from OH and MT for a while.
4. Nate Silver is an ass, but he's right about small dollar donations not mattering for presidential race funding. I give in big enough chunks that I get calls from actual Senate candidates, and my donations are inconsequential at the presidential level.
5. Dems need to make FL or TX swing blue to have a shot at maintaining Senate control moving forward because WV, MT and OH seats will disappear at some point (2 may be gone in November). Plus, if either FL or TX go blue, republican path 270 at any point become super hard.
6. I've donated the most to Mucarsel-Powell this year because I have great personal antipathy to Rick Scott and because I think, with abortion on the ballot, she *should* have a better path to victory. Many of you live in or have deep connections to TX, and Cruz is an easy villain also so please go after him too.