Fifty House Democrats led by Rep. Jamie Raskin (D-MD) have sponsored a bill that would form a commission to assess President Donald Trump's mental fitness for office, pursuant to the 25th Amendment to the U.S. Constitution.
“Some other body” is quoted from the 25th Amendment, which empowers Congress not to do the same thing that the Vice President and Cabinet can do but to create “some other body” that can do what the Vice President and Cabinet can do. They could pass a law that empowers Congress to do that, but that would be less likely to pass than passing a law that empowers some committee because Congress has other things to do.
“Some other body” is quoted from the 25th Amendment, which empowers Congress not to do the same thing that the Vice President and Cabinet can do but to create “some other body” that can do what the Vice President and Cabinet can do. They could pass a law that empowers Congress to do that, but that would be less likely to pass than passing a law that empowers some committee because Congress has other things to do.