Control of the United States Senate is now statistically a coin-flip six months ahead of November’s midterm elections, according to prediction market data compiled by Kalshi, with traders placing the odds at roughly 50-50 between the parties after a dramatic shift in sentiment driven primarily by public opposition to the Iran war and its economic consequences.
Republicans entered 2026 defending their majority with what appeared to be a structural advantage, given the Senate map heavily favoured the incumbent party. What has changed is the political environment, which has deteriorated with unusual speed since US military action against Iran began in late February.
President Trump’s approval rating now sits in the mid-thirties across the major polling aggregators, a level that bank of America economist Claudio Irigoyen described in a Friday note as “having a material impact on policy” given how directly it affects expectations for Congressional composition after November. The war polling is the most striking data point: a Marquette Law School survey placed approval of Trump’s Iran handling at 32 percent nationally, while an AP-NORC poll put the overall approval rating at 33 percent. These are numbers that historically have predicted significant House and Senate losses for the incumbent party.
Senate Democrats face a genuinely difficult map even in a challenging environment for Republicans. Flipping the chamber requires winning in states that Trump carried by double digits in 2024, including Ohio, Iowa, Texas and Alaska. Ohio in particular is being watched closely, where Democrat Sherrod Brown is attempting a political comeback against an appointed Republican incumbent who has yet to face a competitive election. The North Carolina seat, which opens as an uncontested Republican position following Thom Tillis’s retirement, is currently rated as the most likely seat to change hands in the Democrats’ favour, with former Governor Roy Cooper positioned as a strong recruit.
The Indiana and Ohio primaries today are shaping up as the first major test of whether the political environment’s deterioration translates into concrete results. Trump’s endorsement power is on the line in Indiana in particular, where he has targeted seven Republican state senators who opposed his redistricting push last December.
The electorates in those state Senate races are small, potentially as few as 10,000 voters per district, which makes turnout dynamics and local enthusiasm difficult to model. A significant loss rate among Trump’s endorsed challengers would provide an early data point about whether the president’s grip on his own party is weakening alongside his broader approval numbers.
The Bank of America analysis framing the Senate odds as a policy variable underscores how seriously markets are taking the electoral risk. If Democrats take the Senate, the legislative agenda for the remainder of Trump’s second term becomes dramatically more constrained. Even a Democratic House majority alone would shut down significant legislative priorities and introduce a new layer of investigative oversight.
The question financial markets are asking is not whether Trump’s poll numbers are low, but whether they stay low long enough to translate into November results. Six months is a long time in American politics, but the structural forces working against Republicans right now are unusually powerful.
