Rounds vs. Johnson: 52-41As you can see, Herseth Sandlin performs several points better than Johnson in either matchup: She keeps Rounds a hair under 50 and actually edges Noem, the only ballot test where a Democrat leads. Still, this race looks like it would be a very difficult hold for Team Blue even with Herseth Sandlin, and right now, we don't even know who will run. Johnson, 66 and afflicted by health issues ever since suffering a stroke in 2006, still hasn't announced his plans.
Noem vs. Johnson: 49-45
Rounds vs. Herseth Sandlin: 49-44
Noem vs. Herseth Sandlin: 47-48
If he does decide against another go, it's also no sure thing that Herseth Sandlin would run in his stead. She declined entreaties to seek a rematch against Noem last year and instead joined a lobbying firm in DC. That's not exactly the best resume item if you're planning to return home to run again, though Wikipedia notes she never formally registered as a lobbyist, for what that's worth.
If Johnson bows out and Herseth Sandlin says no, that probably leaves Democrats with Johnson's son, U.S. Attorney Brendan Johnson, as their best option, but he starts out with little name recognition and gets crushed by Rounds (53-32) and Noem (49-37) alike. And in a hypothetical (albeit unlikely) primary, Herseth Sandlin starts with a whopping 68-16 lead.
But we may get a bit lucky. While Rounds is undoubtedly the GOP establishment's top choice, he's not a dominating figure amongst the rank-and-file; like most governors, his time in office was marked by a sufficient level of pragmatism to earn him the dreaded label of "moderate" from the conservative base. So even though Rounds announced all the way back in November, the more ideologically pure Noem hasn't quashed speculation about a possible bid on her part, and if she does jump in, hoo boy, things could get interesting.
That's because Rounds holds a bare 43-39 edge in a primary matchup, and Noem actually fares a touch better with GOP voters in terms of favorability, 71-18 vs. 67-17. Unfortunately, it looks like PPP didn't include a question about ideology, so we can't break this down among, say, respondents who consider themselves "very conservative," but I'd be willing to bet that the further right you go, the more enthusiasm there is for Noem.
Now, Kristi Noem isn't exactly Todd Akin, but a messy, bruising Republican primary is definitely possible, and certainly something Democrats would want to root for. And with any luck, PPP's new numbers will help convince Noem to take the plunge. It certainly wouldn't be the first time they've had that sort of effect. And if Johnson ultimately opts against seeking a fourth term, hopefully this new poll will also inspire Herseth Sandlin to run in his stead. After all, she'd have a chance to take revenge against Noem, and how sweet would that be?