The idea of Donald Trump hosting a campaign rally, keeping thousands of supporters in suspense and then pulling back the curtain to reveal that his special guest speaker is Vladimir Putin sounds like a wild hallucination. But not quite as wild as it was a week ago. Trump capped a mind-boggling week by asking his staff to invite the Russian leader to the White House in the autumn, just before the midterm elections. There was a sense in Washington that something had shifted after probably the most damaging week yet of Trump’s presidency – a week in which the word “treason” became part of the conversation.