In the United States, each chamber of Congress (the House and the Senate) has the constitutional authority to expel one of its members with a two-thirds majority vote. This power comes from Article I, Section 5 of the Constitution, which states that each house may "punish its Members for disorderly Behaviour, and, with the Concurrence of two thirds, expel a Member." However, expulsion is the most severe form of discipline and has historically been reserved for serious misconduct, such as corruption, treason, or abuse of power—not for health issues, age, or mental incapacity. There have been only 20 expulsions in congressional history (15 in the Senate and 5 in the House), and none have ever been for medical or cognitive reasons. In practice, it's extremely rare and unlikely to be used that way, as it requires broad bipartisan support and could set a controversial precedent.
There is no specific law or mechanism in the Constitution or federal statutes for removing a sitting member of Congress solely due to mental unsoundness, poor health, or advanced age—even if recovery seems improbable. Courts have refused to intervene in such cases, viewing it as a matter for Congress or the voters. Instead, the main ways a seat becomes vacant are through death, resignation, or the member losing reelection. In cases of severe incapacity, the member's staff often handles day-to-day duties, or the member might choose to step down voluntarily.
Regarding Mitch McConnell specifically, he's still serving as a U.S. Senator from Kentucky, with his current term ending in January 2027. He announced in 2024 that he wouldn't seek reelection in 2026, so he's essentially in a lame-duck period now. As of early 2026, he's 84 years old and has faced ongoing health challenges, including a recent hospitalization in February for flu-like symptoms (from which he was released and is now working from home). He's also had public incidents like freezing during press conferences and falls in prior years, which have raised questions about his fitness. That said, there's no indication of any expulsion effort against him, and based on historical precedent, it's not something that would happen for health reasons alone. If his condition worsens to the point of clear misconduct (e.g., inability to perform duties leading to some ethical breach), the Senate could theoretically vote to expel him, but that's a high bar and hasn't been pursued. Ultimately, voters in Kentucky would have the final say in the next election cycle if he were running again, but since he's not, his seat will open up naturally in 2027.