Betting on Politics: Who Wins the US Senate?

With the key primaries over except for New Hampshire, the dance card for the Senate is set. And so are the odds. Historically, the first midterm election is bad for the president’s party, with the question being not whether there will be losses, but how many.

Polymarket puts the odds of a Democratic sweep (Senate and House) at 49 cents, Kalshi at 46 (Note: All odds are as of the writing of this column). Even so, individually, Democrats are favored in four of the five swing states and Texas as roughly a tossup. Both sites have Michigan and Alaska at 61 cents, and Ohio at 55 cents, favoring Democrats. Maine is at 71 cents on Polymarket (69 cents, Kalshi). North Carolina is prohibitively favored to flip to Democrat.

And here is the issue with betting markets: Because the Republicans in each seat still have decent odds, the market depresses the odds for Democratic control by assuming a decent chance for one Republican to slip through. But elections don’t really work that way. Each election may be an independent trial, but voters tend to shift in some unison depending on national mood.

In short, if a couple of swing states fall, others are likely to follow. But are the odds justified? Both the RealClearPolitics and Cook Political Report Senate maps put all five swing states as tossups; however, the RCP Polling Averages have Democrats leading in each.

Republicans are facing multiple headwinds. The mood of the country is bad, with “Right Track/Wrong Direction” net negative over 25 points. Trump’s RCP approval is net negative 17 points, with even the Trump-friendly polls putting him at least 11 points underwater. His “approval” on inflation (the number one issue) is net negative a whopping 40 points and even the Trump-friendly RMG Research has him down 28 points. By now, inflation opinions can be considered baked in, and a temporary discount in ground chuck isn’t going to change that.

Two issues that could change, probably won’t. Trump’s approval on Iran is net negative over 26 points and trending down. The Iranian leadership seem determined to hold out no matter the suffering of the people. Trump’s new fight with Canada has garnered heavy criticism, even among his supporters. And it won’t help in Maine or Alaska where a June New York Times poll scored tariffs at net negative 23 points and 7 points, respectively. Meanwhile, Canadians back their government at 76%.

Basically, it’s very late to change the national mood. But races still are individual candidates facing off, meaning national opinion is not the whole ball game.

The undervalued race for Republicans is Michigan. Although the Democrat El-Sayed has led in the most recent polls, his numbers are suspect give that he eked out a 1-point primary win despite polling ahead by 10 points. Additionally, as a newcomer, the too-much-online El-Sayed is more likely to gaffe his way through the race than the experience Rogers – who, to be fair, is hardly perfect. However, Trump’s fight with Canada cannot be helpful. All in all, El-Sayed as a 61-cent favorite seems generous.

The bet on control is more complicated than you might think. Democrats need 51 seats, Republicans just 50. But the problem is not election results, it is Alaska Sen. Lisa Murkowski. In my view, Murkowski is a strong possibility to switch sides if the Democrats get to 50 seats (or more). She has already admitted to thinking about it. If she does, there is the question of timing. Murkowski likely won’t switch without a good deal and that could take time.

Polymarket is somewhat ambiguous for the cut-off to determine partisan control, while Kalshi has a closing date of Feb. 1, 2027. The key number is 50. If the GOP drops to 50 or lower, a Murkowski switch could be in play. That possibility puts Republican control in more doubt, and I don’t see that reflected in the current odds. Murkowski could also pad the Democratic majority if the party hits 51 or higher. That also means 50 seats is overvalued when betting an exact outcome.

If you want to bet, I would wager on a Democratic sweep at up to 54 cents, with Kalshi looking to have safer rules. I think Rogers has value in Michigan at 39 cents. There is no chance Republicans gain seats, so betting 95 cents at “No” for 46 seats is a slam-dunk, even if pricey. If the bad news continues for the GOP, a big night could be in store, which would make 22 cents (Kalshi) on the Democrats hitting 52 or more seats a good speculative bet.

As with sports betting, a panoply of outside factors, fumbles, and bad plays could tip outcomes. Picking exact voter percentages and margin of victory is a fool’s errand. The simpler the bet, the better it is.

Keith Naughton, Ph.D., is a partner in the public affairs firm Silent Majority Strategies and is a former Pennsylvania campaign consultant.