After nearly every midterm election following a new president taking office, his party loses seats in the Senate and the House of Representatives. Also called the midterm curse, this pattern is almost as predictable as the change of seasons.
“There is just this general clockwork pattern of midterm decline for the president's party,” said Erik Engstrom, a professor of political science in the College of Letters and Science at UC Davis. “The size of that decline varies and that depends on things like the state of the economy or whether we’re at war.”
In both legislative houses, Republicans hold slim majorities. In the Senate, Republicans have a 53-45 majority, and in the U.S. House they have a 218-212 majority. In the 2018 midterm elections, which followed Donald Trump’s first year of his first presidency, Democrats gained 40 seats and control of the U.S. House.
However, 2026 is unique, with nearly unprecedented efforts to change how voters elect their leaders, including mid-Census congressional redistricting and challenges to mail-in voting. Engstrom, who has published extensively on U.S. elections, said that Republican losses are still likely despite these efforts to stem them.
How could congressional redistricting affect the 2026 midterm elections?
Redistricting involves grouping voters geographically to elect their representatives at the local, state or federal level. While Senators are elected by voters state-wide, every member of the U.S. House of Representatives is elected by voters within their legislative district.
New districts are drawn every ten years after a new U.S. Census, but in 2025, Texas was among the first of Republican-led states to redraw its districts in a way that would tilt the balance of power in the House of Representatives in the Republican’s favor. California responded with its own redistricting plan, which the Supreme Court allowed in February 2026.
As of September 2026, eight of the nine states with new congressional maps were controlled by Republican legislatures, with California as the only exception. Before 2025, only two states had conducted voluntary mid-decade redistricting since 1970
“The number of new maps in the middle of a 10-year Census cycle is pretty close to unprecedented,” said Engstrom. “It's happened before but not to this extent and certainly not in the post-World War II period.”
In June, the BBC reported that it had obtained an internal U.S. House Republican assessment that redistricting had created 10 additional Republican-leaning seats
This year has also seen new challenges to mail-in ballots, which the Supreme Court ultimately rejected in September. A 2025 analysis from Pew Research found that
“It’s an attempt to tweak the mail-in voting rules that they believe advantages Democrats in certain areas of the country,” said Engstrom.
What could the 2026 midterm elections mean for control of Congress?
So far, said Engstrom, polling suggests a decline for the president's party in the U.S. House and also in the Senate, and that if Democrats took control of either the U.S. House and Senate — or both — it would change the political environment entirely.
For example, if one or more Supreme Court justices steps down, a Democrat-controlled Senate would make confirming the President’s nominations much more challenging.
Engstrom also said that, while unlikely, it’s still possible that Republicans maintain control of one or both houses of the U.S. legislature. However, he does not expect governance or party politics to change dramatically in the next legislative session given a likely narrow majority.
“They’ve been able to get some big things through, like the One Big Beautiful Bill Act, but it’s also been a fractious two years even within the Republican Party itself,” said Engstrom.
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