The biggest suspense of the US midterm elections: Republicans unexpectedly hold the Senate vs. Democrats winning 53 or more seats.

Title context: The biggest suspense of the US midterm elections: Republicans unexpectedly hold the Senate vs. Democrats winning 53 or more seats. Text: With less than a week to go before voting day, control of the Senate has become the most critical variable for US equity market direction. Citi believes the blue sweep expectation has largely been priced in by the market, and the real market risk lies in two tail scenarios: Republicans unexpectedly holding the Senate, or Democrats outperforming expectations and winning more than 53 seats. Citi Research noted in an October 30 US equity strategy report that the probability of Democrats sweeping both chambers is already the highest-probability scenario and has continued to climb recently, and this expectation has to a large extent been incorporated into current US equity valuations. However, polling results for several key Senate seats remain within the margin of error, and it is not impossible for Republicans to hold the Senate. Citi strategists Scott T Chronert and Patrick Galvin believe that if Republicans hold the Senate, US equities could receive an additional boost by year-end; conversely, if Democrats win more than 53 seats, the market will begin to price in ahead of time the risk of a corporate tax rate increase in the 2028 election, putting pressure on equity valuations. The two scenarios point to diametrically opposite market directions, making the Senate election outcome the core driving variable for US equity market performance next week. The relative performance of the financial and healthcare sectors, the pace of AI data center construction, and the outlook for 2027 budget and debt ceiling negotiations will all face repricing due to the election outcome. Senate suspense: a tug-of-war within the margin of error The probability of Democrats flipping the Senate has continued to rise over the past few months, and this week, as early voting data were released one after another, momentum in prediction markets shifted further toward Democrats. However, Citi emphasized that this outcome is far from certain. In terms of seat distribution, excluding swing states, Democrats are currently projected to secure 53 seats and Republicans 47. But as many as 16 key Senate seats are listed by RealClearPolitics as in competitive toss-up status, of which 9 are "true swing" seats. The latest data from prediction platform Kalshi show that Democrats currently lead in key seats such as Texas (D +72%), Michigan (D +74%), and Ohio (D +70%), but the advantages are not overwhelming. Seats such as Iowa and Nebraska are still narrowly led by Republicans. Citi noted that if polling in multiple swing states simultaneously shows systematic bias, the results could very well tilt entirely toward one side, causing the final Senate map to swing sharply from "Republicans hold" to "Democrats greatly outperform expectations." Trump's approval rating is a key reference for understanding this backdrop. Citi data show that Trump's current net approval rating in this governing cycle is about -21.7%, one of the lowest levels for an incumbent party candidate entering midterm elections in nearly 20 years. The generic ballot currently shows Democrats leading by about D+8.1, similar to D+7.3 in 2018. Citi believes the current setup is most similar to the 2006 midterms under George W. Bush when Democrats gained a net 31 House seats and a net 6 Senate seats, completing a flip of both chambers. The House is already settled; the Senate is the key On the House side, Citi basically concludes it will flip to Democratic control, and this outcome has been fully anticipated by the market. Republicans currently hold only a narrow majority, and it is historically normal for the governing party to lose House seats in midterm elections. Citi believes the marginal market impact of the House outcome itself is limited; the key lies in the magnitude of the Democratic seat gain. If Democrats control the House by only a narrow majority, lawmakers will be forced to vote strictly along party lines; if Democrats win by a larger margin, some lawmakers will have more room to flexibly take positions on key issues based on constituency interests, which would marginally increase the probability that Democrats retain those seats in the 2028 election. In other words, the larger the Democrats' midterm victory margin in the House, the higher the probability of achieving a "blue sweep" in 2028, all else being equal. The Senate situation is much more complex. Citi specifically noted that Senate terms are six years, and this midterm election's seat advantages will directly affect the Senate control landscape in 2028. In 2028, most of the seats Democrats face for re-election are in safe districts, so if Democrats can win more than 53 seats this cycle, it will significantly raise the probability of maintaining a Senate majority in 2028, thereby increasing the likelihood of Democrats achieving a full sweep. Market impact: two scenarios, two logics Scenario one: Republicans hold the Senate Citi believes that because the market has already priced in a relatively high probability of a blue sweep, an unexpected Republican hold of the Senate would constitute a positive surprise and trigger a year-end rally in US equities. At the sector level, Citi's previously recommended relative value strategy of "long healthcare/short financials" has largely played out. If the Senate election result is favorable to Republicans, it will become an increasingly important trading driver for the financial sector, because Senate committee leadership can influence the direction of financial regulatory policy, and the Senate also has the power to confirm Federal Reserve governor nominees. After Powell's term expires, the appointment of his successor will also be affected by this mechanism. Scenario two: Democrats win more than 53 seats Under this scenario, Citi expects US equities to face incremental pressure, spanning both short-term and medium- to long-term horizons. In the short term, market sentiment will come under pressure; in the medium to long term, investors will begin to price in ahead of time the risk of a corporate tax rate increase in the 2028 election highly consistent with Democrats' policy proposals in the 2024 election. Citi also noted that 2027 budget and debt ceiling negotiations will return to focus: Democrats may push to restore healthcare spending, while Republicans tend to increase defense spending, and deficit expansion pressure will rise, although the positive effects of fiscal stimulus can partially offset this. AI data center construction may become an additional variable Citi specifically noted that gubernatorial and local election results may have spillover effects on the pace of AI data center construction, which investors need to watch. Prediction markets show Democrats may make gains in multiple gubernatorial elections, including Wisconsin, Ohio, Michigan, and Nevada. Democratic governors generally take a more cautious stance on data center construction permits and zoning planning, which would marginally increase administrative obstacles to advancing data center projects. Citi highlighted Texas as an example: although incumbent Governor Abbott (Republican) maintains a certain lead in polls, declining support for federal Senate candidate Paxton (Republican) creates the possibility of ticket-splitting, which has already put Texas into competitive status. If Texas ultimately tilts Democratic, its impact on the AI construction investment logic would be the most representative case among single-state dynamics. Citi also emphasized that the above pressures are more a reflection of extended supply timelines rather than cancellation of existing data center construction plans, so the impact on the industry's long-term fundamentals is relatively limited. In addition, a Democratic government's concerns about infrastructure financing pressure may actually ease somewhat, providing a partial positive offset on the construction funding side. Election results do not change fundamentals, but will reshape sentiment and expectations Citi ultimately concludes that the midterm election results are unlikely to have an immediate impact on US equity fundamentals; swings in sentiment and policy expectations are the main market transmission mechanism. If Republicans hold the Senate, Citi expects a phased rebound to be triggered, and this scenario is still not ruled out; if Democrats sweep both chambers, it would be marginally negative in the short term, but the magnitude is closely related to Texas. If Democrats ultimately win more than 235 House seats and more than 53 Senate seats, the market will have to take more seriously the scenario premium of a 2028 corporate tax rate increase and full Democratic governance. This article is reposted from "Wall Street See" (Wallstreetcn), author: Zhang Yaqi; GMTEight editor: Xu Wenqiang.