Manchin is probably in trouble - but it also depends on who Republicans nominate. I think Manchin is toast if he faces Evan Jenkins, he's in for a battle of his life against David McKinley or Patrick Morrissey but could win, and he's probably fine against Alex Mooney, Mac Warner, or *giggles* Bill Cole. I'd give this a Toss-Up, maybe even Tilt R because I doubt anyone from the "losers" category jumps into the race.
Heitkamp is not to be underestimated, but it'll be tough. The earliest suspected opponent for Heitkamp is Rick Becker - who was a candidate for Governor this year and tends to think of himself as libertarian. I doubt he gets the nomination. This is definitely a fascinating one to watch. Tilt R.
Tester benefits from Montana Democrats being awesome at elections, but also has to face midterms which are historically tough. The problem with Montana's Republican bench is that they're all empty suits - Ryan Zinke on down. Daines got incredibly lucky and still only won by 15 - which just isn't a great margin for a Republican in a deeply Republican state. This will be a single digit race either way, total toss-up.
I'd definitely be surprised if Donnelly won re-election. He hasn't made a strong impression either way, which can be good if you're like Portman, or can be bad if you're like Kirk. Somehow I think Donnelly ends up a bit more like Kirk. Plus Indiana has a dense and solid Republican bench. This is at least Lean R.
McCaskill is a rough and tumble campaigner but I think her days are numbered - I almost hope that she drops out and gives Kander another chance at a Senate seat. This seat is probably Lean R with McCaskill and Toss-up with Kander.
Sherrod Brown's politics may not jive with the new right-of-center leadership in the state, but I think it works in the areas that Clinton lost badly to Trump this time around. It'll be a tough fight either way, and I'm hoping somehow Mandel ends up sneaking away with the nomination because he proved to be a punk in the 2012 Senate race. Toss-up without Mandel, Tilt D with Mandel.
Nelson is probably fine as long as he's in this seat, but I'd proceed with caution. The reason? Carlos Curbelo. I think he's a strong rising star in the Florida Republican Party, can sway Miami voters who dumped Trump but fell in love with Beautiful Wonderful Amazing
<3<3 Marco Rubio, and won re-election by a considerably wide margin even considering this years circumstances. I think he's the only Republican who could knock off Nelson. Lean D if Nelson stays, Tilt R if Nelson retires.
Casey is deeply uninspiring but is probably fine against any Republican challenge. I'm not sure who the bench here is for a Senate seat atm - Brian Fitzpatrick? Ryan Costello? maybe even someone lower on the list like John Rafferty? Something tells me he wants to go for Governor, but I suspect Wolf stays on to run for a second term, much to Casey's dread. Lean D.
Baldwin and Stabenow both strike me as functionally competent incumbents who will survive even if this becomes something of a bloodbath. The best Wisconsin Republicans can do is either of Scott Fitzgerald, a Scott Walker cheerleader, or Sean Duffy, a man who will be exposed as a clown when he runs for an office beyond a congressional seat. The best Michigan Republicans can do is... umm, someone help me out here? whoever the Lieutenant Governor is? one of the many congresscritters? someone we don't know yet? Likely D for both.
How many survive? 4, 5, maybe 6 if I'm being optimistic.
