“The historical pattern is clear, and ominous for Joe Biden and Democrats this year: The president’s party usually does poorly in midterm elections.”
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“Some theories focus on lower turnout among the president’s supporters. Others emphasize the public’s tendency to sour on an incumbent president. They may both be correct to some extent.
Other theories focus on why some presidents tend to do worse than others in midterms. Maybe the results are mainly about presidential approval these days. Or maybe they’re about the economy or, more specifically, real personal income growth. Some national crises, like 9/11, are associated with unexpectedly strong midterm performances for the president’s party — but others are associated with blowout defeats.
None of these signs are looking great for President Biden right now. His approval rating is the second-lowest of any president’s at this point in their presidency since modern polling came into use. The economy is booming by some metrics, but inflation is at a 40-year high and eating into voters’ spending power. The country is still in the midst of the pandemic, but Biden hasn’t unified the country around his leadership.
There’s no one weird trick that can guarantee midterm success, or one theory to perfectly explain every midterm result. But there are several that, considered together, go a long way toward helping explain why this so often happens — and what November’s midterms might herald for Biden.”
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“The trend predates World War II, so it’s not about recent developments. It happens in states (the governor’s party usually loses seats in off-year legislature elections), so it’s not just about the presidency. It’s not just an American phenomenon, either. “It also occurs internationally in systems where there is a chief executive election separate from a midterm,””
https://www.vox.com/22899204/midterm-elections-president-biden-thermostatic-opinion