Johnson knew that his name would be mud if he did this. I presume he saw the opportunity to seize the moment, sell out his side and get a payoff that enables him to enjoy the rest of his life after he is retired from the house. Hell, I would put even odds on him retiring at the end of this term like all of his other fellow RINO have been doing.
That seems to be the norm with Congresssional Republicans these days. I won't be voting for my GOP Rep. in November. He's running for his second term, and has voted regularly to send money to Ukraine, voted for the last expenditure Bill, and voted twice this past week to keep FISA.