I think it's unreasonable to take the literal meaning od 'anytime, anywhere'. Like, if he was attending a funeral and the senator turned up and challenged him there, would that still be appropriate? How about if he was visiting a kindergarten? While he's helping an old woman cross the road? Performing first aid on an injured person?
There are still times that are appropriate and not appropriate. You could say that the challenge itself was childish and I would agree. But the anytime, anywhere condition doesn't make it unconditionally ok for the senator to pick this time and place.
Honestly I agree. I just don't think that excuses the Senator from actually accepting the challenge at that time and place (or arguably any time and place, but especially that one). Two wrongs don't make a right...
The choice of time and place is irrelevant when the instigating party said, and I quote, "anytime, anywhere", and then when their challenge was accepted, stood up, ready to engage in said challenge.
In response to people saying that the Senator acted inappropriately. But perhaps I misinterpreted. Are you saying they both acted inappropriately? In which case I agree, but I'd still say tweeting a challenge is less inappropriate than actually accepting that challenge at that time and place.