Trump is a germaphobe - yes he does sometimes have to shake hands but does so reluctantly - not shaking someone's hand does not mean they "refused" to however. I don't like pineapple on a pizza and find this easy to avoid so I don't have to refuse to eat it. Maybe Merkel didn't know of Trump's phobia or just forgot. Or Trump had shaken so many hands on his recent travels that he was protecting her from his germs - he can't use the White House bathroom to wash his hands because there are bugs in it.

Or maybe the handshake incident never happened in the first place (or second).