Well, crap. Where’s an originalist when you need them? You’d think this SCOTUS would be happy to say that all the clause protects is speech while acting as a member of Congress.
Hmph. 
The way I’ve always remembered (since I was a kid) is that “libel” sounds like “library” so involves things written down.
And so slander is “the other one”.
(and because this is the final ever, ever pedantic nitcpick post I’ll ever post again)
Statements can frequently be written, like in contracts, etc.
I’d replace it with “Say”.
All the other S and L’s are splunge/cromulent.
Piling onto the nitpick…
How about Speak?
How most of this court rules would depend on the letter behind the lawmaker’s name.