I believe he is still a Senator in the United States Senate. I believe that it is the job of Congress to provide a critical check and balance of the Executive. I believe that the Senate is actually part of Congress.
Tell me why, again, that we shouldn't listen to him?
I believe they still teach "checks and balances" in US Government classes, since it's pretty much a founding tenet of our democracy.
Not to mention, regardless of loss, half (or nearly half, depending on who's doing the counting) the country actually wanted this man to be President. It's not chess or checkers, the "loss"doesn't mean the loser gets taken out and shot, they are still breathing, they are still American, therefore, they still are allowed to speak their mind.
One failed Presidential election bid does not obviate somoene's opinion or ability to actually say somethign meaningful.