What's the 25th Amendment, and how would it be invoked?

After chaos erupted at the Capitol on Wednesday, some are suggesting that the president should be removed by invoking the 25th Amendment.

House Speaker Nancy Pelosi, Sen. Chuck Schumer, and other Democrats have called for the 25th Amendment to be invoked against him. Secretary of State Mike Pompeo and Treasury Secretary Steven Mnuchin reportedly held informal conversations within their agencies about the 25th Amendment and how it would be invoked, according to CNBC.